After importing our old wiki, users cannot get their accounts back because they're told they already exists. It's already been discussed:
I was also told to use Special:GlobalRenameRequest but that only works for logged in users. So I told users to create a temporary account and use that to open that page, but it still won't work because the requested name already exists.
So, how does this work, exactly?
For example, user Revenant Lord created Revenant Lord temporaneo as a throwaway account, and now he needs to get back his original account. Let's assume you just merge them, do I have to ask every single time? It's not a problem because there's not that many users wanting their accounts back, we just need to know how it works.