Do account names expire?

I opened an account briefly last year to communicate with my lawyer.  I decided today to go into it and make certain everything is deleted. I've forgotten the password so asked that a reset link be sent to the secondary account assigned to this account. When I looked closely I realized that what little I could see of the secondary account (most of the name is not visible of course) didn't look at all familiar to me and I don't even remember the full name of it. But clearly I set it up because there it is, and now I can't access it either. I can live without both of these accounts, but since it's been a year I wonder if account names expire. Specifically, might someone else have been able to select and use the name I had on the secondary account, and therefore received my reset link for the lawyer account?