You have to be logged in and, if I understand correctly, if you don't log in to old.reddit for six months (retroactive) they take it away.

My understanding (just from chatting with Gemini) is you just need to visit reddit (logged in) within the past 6 mos and don't have to log out/in again or anything like that.

So basically, I probably have a bunch of accounts from years ago; suspect that all but my current one no longer work with old reddit.

Biggest annoyance for me would be on mobile where i wouldn't log in.