Would be basically impossible. Most of what is leaked these days is just rebundled from other leaks. For example if you listened to MB on this its only a small % of data from new leaks that actually ends being new info.
Any attempt of doing something like this would prove to be trash data pretty quickly and would not have a major effect.
It sounds like they just report the number they are sure of at the time and update the filing later. Very high chance the number of affected is much more then 1.3M - the number of unique email addresses alone makes it pretty clear its more.