You need to make a new account to play TLOPO. Though the game is made up from the original POTCO game the old accounts were not included in this release so get stuck in with a new pirate and enjoy TLOPO beta!
I don't know the technical details of the game by no means and I'm sure if you require more in-depth details a staff member will answer your questions better
I highly doubt Disney ever would have or would ever release the account information for POTCO.
For TLOPO to have acquired that, they wouldn't just be giving TLOPO the pirates and their information - they would be giving TLOPO everyone's registered emails, usernames and passwords. This is not something players signed up for, which means Disney would be facing a potential (and massive!) lawsuit.
Even if they were legally protected, there's a major ethical concern here. Many people use the same passwords for multiple stuff. Handing that information over to TLOPO (even if encrypted - all encryptions can be decrypted, especially if TLOPO was supposed to actually use it!) would be handing TLOPO all the email addresses and passwords to those emails for a lot of people. Many other sites/games accounts use emails for password resets. You could argue that it's the users own fault, but that argument is quite irrelevant. This isn't a risk Disney would take.
That's to say this info is still even stored anywhere. It could be long gone by now. Edit: Unless it's a disney-wide account, as @Kris mentions below.
TL;DR: Major security concerns involving emails and passwords. Disney would never hand any other party their playerbase account information.
To add to this; a POTCO account is basically a Disney wide account which still exists after the closure of POTCO and Toon Town. I found this out one day when I logged into ESPN.com (owned by Disney) using my POTCO log in. The pirates...etc from POTCO do not exist anymore but the accounts are there.