That's still worrying me--since they changed the SE website, my profile doesn't appear to have anything registered on it (though the SE Members page does show it, though it takes forever to find that spot). When I go to register just in case, it gives two options for the code type:
XXXXXX - 000 - XXXXXX - 000 (6 letters + 3 digits + 6 letters + 3 digits)
XXXXXXXX - 0000 (8 letters + 4 digits)

However...my registration card's code has a format: xxxx-xxxx-xxxx-xxxx, where it can be either numbers or letters interchangeably.

I'm doing my best not to freak out just yet, but if this stops me from logging in on release I'm going to be pissed.