yes, I want option to mark “I went there, I surveyed location, I was unable to change entrance=yes into something more specific”. It could be an extra tag or new entrance value.
And yes, I want this to make possible surveying this with StreetComplete (though could be also used by other tools listing places worth surveying)
Then creating a new value of entrance=* instead of using a prefix/suffix like check_date sounds like a bad idea, because you’d want to have a general solution, while a new value would only solve this one use case.
On the other hand, just because you were unable to classify an entrance into something more specific doesn’t mean no one else would be able to. Would you stop showing a SC question to other people, because a single person wasn’t able to answer the question?
If the goal is to stop asking you the same question over and over again, that should be implemented in the SC application, by remembering that you (as a user) are unable to answer the question and don’t want to see it again, but not by means of tagging this in OSM.
@Nadjita: now please have a little more understanding for the users of StreetComplete, who are asked the same question over and over again. 
(I can’t decide right now whether I should be amused that people come up with such ideas at all, or annoyed because with the help of SC the database is increasingly filled with things that are actually default, but SC can’t distinguish whether it has already been checked on site and found to be default or a more specific entry is simply missing).
Just to avoid misunderstandings: I use StreetComplete myself. But sometimes … argh.
It’s a general thing in OSM: you can’t tell the difference between unsurveyed, surveyed but not an approved type, and surveyed but I don’t know these things. I don’t think classifying it as unclassified would solve this any time soon, and I don’t think we should invent tags for individual cases to tell the difference. It’s not an attribite of the entrance that the mapper doesn’t know the type, and it’s not a mandatory tag so you can’t force mapping it.
Tools should find their own way to deal with that. If a question keeps bothering the users, find a way to allow them to stop getting this question.
So, 37 and 39 you’d map as entrance=staircase.
If I understand correctly, 37a does not have a staircase, so you cannot use that value, OK.
But what is wrong with marking it as entrance=house defined as:
Door to a private house, home or an apartment.
If that is indeed entrance to residential house/apartments as it looks to me on first sight?
Or even entrance=main defined as:
The main entrance of a building or enclosed area.
because it does look as a main (maybe even only?) entrance to 37a part of the structure (if it is not residential)?
And while talking about it, I find entrance=staircase badly defined. It says just “A staircase entrance, almost always a door” which does not help much. Ok, most of the entrances to buildings are doors, so that does not seem specific. But neither is “A staircase entrance” really any more descriptive than entrance=staircase.
Only picture on entrance=* wiki helps a little (surprisingly, picture at supposedly more detailed entrance=staircase does not help at all!) - it seems that after a door is opened there are stairs. But do they lead to single private home (eg. building=home)? Or to a many different households (e.g. building=apartments)? Or it doesn’t matter and it can lead to both private homes and condos?
And do stairs have to be after the door, or can they be before door (or both before and after?). Do the stairs even matter, or can it be just a step or two (e.g. if it is single-floor apartment building)?
And if stairs must be there, must they begin immediately after the door as in that picture, or can there be a short hall (e.g. containing multiple postboxes) before stairs? (as is most common case in Croatia for multi-floor apartments buildings / condos, for example)
And while talking about it, I find entrance=staircase badly defined.
I agree, it isn’t clear from the pictures either because of the photo on the entrance key page (which seems to show an internal staircase of a single dwelling), and it misses indications when to use it (because almost any multistory building will have its entrances somehow leading to staircases so there is significant overlap with main and yes).
I think that for residential buildings we should map only the entrances as such anyway (entrance=yes). @dieterdreist is right, with multi-storey residential buildings there is always a staircase somewhere behind it, unless it concerns individual flats (or shops) on the ground floor or in the basement.
I think the distinction was once meant for public (publicly accessible) buildings like office buildings and shopping centres. There it is also important to distinguish between main entrances, entrances to stairwells, staff entrances, supplier entrances and escape routes.
In residential buildings, main entrance and entrance=staircase are synonymous for me. At most, one can still differentiate between entrance=home for direct flat entrances and entrance=shop for direct entrances to shops. I personally would not use service entrances (mostly direct entrances to the basement) in residential buildings.
If I compare your green marked entrances to: Key:entrance - OpenStreetMap Wiki all three would be entrance=home. I agree with @Matija_Nalis that entrance=staircase isn’t a suitable value-definition, as it gives no information regarding the purpose, like all the others are doing. But even though, it’s not reflecting your doors, which have the stairs outside.
The door between 37 and 37a looks like entrance=shop where the door between 37a and 39 looks to me like entrance=maintenance.
In summary: I rather would add more purposes for entrances than a second “yes”.
I agree that the wiki description is not clear. My understanding is that the type of entrance is based on what it lead to or way from. So a main entrance usually leads to some type of a lobby or central area. A service door would lead to an area designed for building staff to gather before going start their shift.
Using the same logic a entrance=staircase should be a door that leads directly to a landing with stairs or elevator bank. There should be nothing else directly accessible from this door. If there are connected rooms or other hallways than the entrance should be considered secondary.
agree that the wiki description is not clear. My understanding is that the type of entrance is based on what it lead to or way from. So a main entrance usually leads to some type of a lobby or central area. A service door would lead to an area designed for building staff to gather before going start their shift.
IMHO the “entrance” value is referring to the type of entrance, only loosely connected to the kind of area it leads to. You could have a service entrance leading to the main hall (as a secondary entrance) but likely not a main entrance that only leads to a service area.
I guess we can agree that the wiki needs a bit more clarification and examples. For example, I was under the impression that for an apartment-block, the “main” entrance would be entrance=main, but nowadays, I more or less just tag it with entrance=staircase. But I wouldn’t consider any of them “wrong”. The main entrance might very well lead to staircases, right? It would really help having defined examples and guidelines what’s used for what, because right now, I always have the feeling I’m picking the wrong one 
The only entrance values which were in the original, approved proposal are yes, main, service, exit, and emergency.
In particular, the key was not intended to to contain information about what the entrance leads to (a shop, a home, …). These are all later additions which I believe degrade the logic of the key and should not have been allowed to be added.
The situation of “how do I map the main entrance to a home” could easily have been avoided, for example by introducing a second entrance_to key. (And in many cases, this information is already implied by the tags of the building the entrance node belongs to, so it doesn’t need to be tagged anyway.)
People started using entrance=staircase as apartment building may have for example 7 entrances, each to staircase going through all levels.
Calling such entrance “main” seems weird and incorrect, to the point that people invented new tagging.
So each of 7 entrances leads to the same set of apartments? Or each staircase to different set?
I still don’t know what is really meant by entrance=staircase, see my questions above. What they mean to you?
Hmmmm, to me it seems normal usage in English (but I’m not native speaker).
Do you mean it sounds strange because there are multiple main values, or something else?
It looks to me it is OK usage, e.g. MAIN Definition & Usage Examples | Dictionary.com says:
adjective
chief in size, extent, or importance; principal; leading:
the company’s main office;
the main features of a plan.
So if there can be “(multiple) main features”, then there can also be “(multiple) main entrances”, right?
The only reason to have multiple main entrances is because they all lead to same common area. For example some large building with a large front desk area. On the outer edge there are usually stairs and banks of elevators that allow access to the rest of the building. The area is often large enough to occupy most of the ground floor. Whether reachable via hallways or not. It is accessible from multiple sides of the building.
I can imagine a large apartment building that has seven entrances.
However, it is difficult for me to imagine that all entrances have the same house number and that all flats are equally accessible via all entrances.
Isn’t it much more the case that each of these entrances has its own house number and therefore each entrance can be an entrance=main?
Why should this be wired and incorrect?
I can imagine a large apartment building that has seven entrances.
However, it is difficult for me to imagine that all entrances have the same house number and that all flats are equally accessible via all entrances.
both situations exist, entrances which lead to a single staircase and no internal connections or common connections inside a building.
The latter is typical for higher buildings as fire regulations usually require 2 different escape routes, and in lower buildings the second route can be through the windows and fire department ladders while high-rise buildings usually require additional staircases (and entrances).
Isn’t it much more the case that each of these entrances has its own house number and therefore each entrance can be an entrance=main?
house numbers are not necessarily related to entrances, it depends on the area/region. A distinct house number doesn’t generally imply it is a main entrance.
In Poland it is typical that building has a single house number, multiple entrances and each of entrances leading to a separate set of apartments.
See say Way: 155371285 | OpenStreetMap
There may be connection between staircases but often is not typically used.
numbers displayed on entrances show ranges of apartments accessible through a given entrance (top-left entrance had its sign missing so data is missing for now).
Calling every single out of this six entrances a main one seems a bit weird to me.
Usually different one.
Sometimes you can get between staircase by basement corridor or corridor in attic, but both are basically unused and may be restricted to use only by residents.
So you need to use matching entrance.
Yes. Also, because saying that half of entrances (or every single entrance to a building) is “main” seems suspect.
Kind like saying “these things are our priorities” and proceeding to list every single possible goal, direction and project.
I am not either.
Though listing every single feature of a plan as a main one seems suspect.
