Comment by pvg

printed Bulgarian only uses that form

This is a total pedantitangent but I don't think that's actually true. These wikipedia pages don't talk about it directly but I think give a bit of the flavour/related info that suggest it's not nearly that set in stone:

https://bg.wikipedia.org/wiki/%D0%91%D1%8A%D0%BB%D0%B3%D0%B0...

https://bg.wikipedia.org/wiki/%D0%93%D1%80%D0%B0%D0%B6%D0%B4...

The second one, in particular, says early versions of Peter I's Civil Script had the g-looking small д, so these variants have been used concurrently for some time.