I don't know about the state of the abandoned railway. I just noticed that there is no relation yet for this former railway line, so I created on. I also connected it with Wikidata. Feel free to add or remove tags to the relation. I did not change things for the tracks.
I don't know why the layer went wrong. I removed it now.

Yes, I meant uic_ref. Thanks for your fix.

> it can hide the StreetComplete address quest for the building

I am an "excessive" StreetComplete user (was once even #1 user in Albania :-) ) and don't see this. However, SC is just one app, there are many more. I also reported already several bugs to SC to help improving it.

You have not replied to my main point: I map to:
* benefit personally to later find addresses, routes and info (I now live here)
* to help the shop owners

For both it is important that the info is available and there is no reason why the house a shop is in should be used to provide info. This info: house address is also shop address might be true for Sofia, or maybe not or maybe not for all Bulgarian municipalities and what about in general? No app in the world can find out that local rules might apply (house numbers, PO-box numbers). Therefore mappers should be encouraged to collect as much info as possible.

And again, if a shop closes, the node can simply be removed or changed to the successor. If a shop moves, of course a node must then be updated - updated location is logically also an updated address.

> Once address data is duplicated, future mappers need to keep it consistent - and in practice, this often doesn’t happen. For example, if a notary moves to another location, the node might be moved, but in many cases the address tags remain unchanged,

This cannot be an excuse not to add addresses. It is simple wrongdoing to move a node and not updating it. This contradicts the idea of OSM in my opinion.

> An address is a property of the building (or more correctly for Bulgaria

But some of my business partners use post boxes, thus the official address (the one in the trade register) is on that post box, thus independent of e.g. the main office's location.

However, the main issue remains - independent of a city an its particular cadastre rules, web crawlers should get info about shops. The shop owners want to get found and the apps want to provide users e.g. how to route to a location. It is impossible for a crawler to know in advance that Sofia has the rule that if a node is inside an OSM area having a house number, the shop always has the same number, while in Shumen it might not be the case. Or take Berlin where on some areas shops with entrance at the backside of the house gets the suffix "b" while shops with entrances to the main street get "a". Or in Tirana (I lived there) the official address is the number of the entrance of a building. So the house has e.g. number "53" but the official address of my company there is "53/1" (and as funny as it is, there is no "53/2" only a 52/3.

Should apps like OSMAnd~ learn all cadastre rules of all countries? (and in e.g. Germany even every municipality has its own numbering rules)

To osm.wiki/One_feature,_one_OSM_element:
there is nothing written that one should not also add the address to shop nodes.

By the way, I only add the address if I know it for sure. I most cases I take the one given at the website of a shop because (in others I take the one from business cards I got) this is the only way to get it right.