The help article I accidentally created two accounts; how do I merge them? indicates:
If you have two accounts that you would like to join together, please edit the ‘about me’ section of each profile to say “merge keep” and "merge delete" and then contact us. You will need to provide links to the two profiles you would like to merge - we'll merge the one you annotated "merge delete" into the one you annotated "merge keep".
If you can't remember how to log into one of your accounts, go here and enter the email address you used to create it.
So, as long as you've used a valid email address for previous account, you might be able to recover it (and help speed up the merge process).