Board Thread:Support Requests - Getting Started/@comment-24175073-20131223101411/@comment-366087-20131223103238

Have you tried the "I forgot"? options at login? (actually, I'm always logged in, so I forget if there is one, and what restrictions may be on it).

Staff cannot help you with passwords, but if you contact them via Special:Contact they might be willing to perform a checkuser on you to determine if you are the same person. Then they might help you with the email attached to the old account.

Otherwise, they'll probably advise you to adopt each of your old wikis in the standard manner.