”This map is for informative purposes only, cannot be used in any official application procedure.”
This is a map published by the Metropolitan Council financed by us, the taxpayers. But think logical: no one can impose copyright on street numbers. Anyway, how will you decide whether I pasted the house numbers based on a site visit or using an on-line map published on the internet?
The law may not always appear logical to laypeople such as ourselves, but this topic has been discussed previously and some interpretations say that the European Database Directive, or national law in certain countries, may indeed cover collections of facts - even if the facts themselves are not individually copyrightable.
So general policy is to use only sources where the owners have explicitly granted permission to use it for OSM.
And unfortunately, a lot of data paid for by taxpayers is nevertheless not released under a free license. 
Almost all databases contain errors. Often it’s very unlikely to make these errors after a visit on the ground. And if a source you previously mentioned in a forum post happens to have the exact same errors, then the conclusion is pretty obvious…
I only edit the map section in my neighbourhood, so that map is only a reference for me. City Council clerks will not come here and compare their map with ours using a magnifying glass. Moreover, I do not automatically follow their map, but only make changes on OSM after on-site visits.
You know, I live in a pretty nice residential area and make my everyday 5 to 10 kms walk for several years by now.