Do sealed beta eggs keep their stats at launch?

That matters most if you spent beta time chasing quality. A sparkling creature stays sparkling. A perfect one stays perfect. The stat spread and skill set it had in the beta are the ones you get on the other side, so none of that work has to be repeated on the global build.

The catch is in the timing, not the stats. A sealed promise egg cannot be hatched the moment you claim it. You first have to unlock that Aniimo's form in your Anilog by going out and catching the basic version of the same creature. Until you do, the egg sits there. Catching the basic version is only a key to the lock, though. It does not set what comes out of the egg, and you are not re-earning sparkling or perfect status by doing it.

Getting the egg in the first place

Preserved creatures do not travel with your account automatically. If you secured a creature in the beta, you claim it as a sealed promise egg through the official event page, signing in with the beta account that caught it. That claim is the transfer. No claim, no egg.

Other eggs at launch

Sealed promise eggs are not the only ones you will be holding early on. Global launch rewards include eggs of their own, among them a free Perfect Egg. Those are separate from anything you carried over, so a returning beta player starts with both piles.

Not settled: The preservation rules here describe how the system worked in the closed beta, and the handling of carried-over creatures can still shift before the global launch build is final.