Sounds like the perfect time to revoke the credentials and find out what uses them, so we can find why they weren't registered as credentials in use. Personally I'd rather do that, have a team ready, and break production for x minutes in order to properly register auth keys.

I'd definitely consider a "silent" credential - a credential not registered centrally - to be a huge red flag. Either it could get stolen, or break and no one knows how to regenerate it. And it's pretty easy as devs to quickly generate an auth key that ends up being used permanently, without any documentation.