Unfortunately the OSM website has a limit to how many it can show you at once and it shows the most recently updated ones, so you can’t see how many unclosed notes still exist.
One of them is over five years old and requires on-site verification, so I know what I’m doing this weekend!
Looks like it might have been case sensitive.
Oh yes, osm usernames are strange: they can also contain any unicode characters, spaces, emojis, and you can change them anytime. I don’t know any other site where username requirements are these lax.
There were already minor abuses, a troll registered as the username of a DWG member, but replaced one letter with a homoglyph. E.g. these are different unicode letters:
oоοJust copy them to a unicode decoder.