I have seen that in the wiki are strikethrough out and do not advise using the type of surface cobblestone:flattened to avoid confusion with sett and unhewn_cobblestone.
I think that in the discussion did not take into account a way of making pavements that is used in the south of Brazil and northeast of Argentina (see in overpass: http://overpass-turbo.eu/s/x19 ), which is called “brazilian cobbled style”, which is a variant of the known as portuguese pavement (see: https://en.m.wikipedia.org/wiki/Portuguese_pavement ).
The brazilian cobbled style is made with basalt stone and fits what can be defined as “cobblestone:flattened”: natural stone, crushed, smoothed surface, irregular, binder witk earth.
As you can see in the images:
https://wiki.openstreetmap.org/wiki/File:Empedrado_brasilero_1.jpg
https://wiki.openstreetmap.org/wiki/File:Empedrado_brasilero_2.jpg
For this surface, I think that the type sett (stones with regular format) or unhewn_cobblestone (uncut, with rigid binder) is not suitable.
For this, I request that consider modifying the wiki and not removing the “cobblestone:flattened” option to be able to use it on brazilian cobbled style pavement.