No, the difference re those suits is that there would be standing. A specific harm to specific persons.
The difficulty (IMO) would be presenting sufficient evidence to get to the discovery phase. It would be ‘proving a negative’.
I could be wrong and am certainly NOT claiming infallibility on this incredibly complicated issue, but...I believe many of those Vietnam era suits were filed by individuals trying to escape service; an individual suit for an individual circumstance. And yet, those too weren't even heard for "lack of standing". That's the courts catch-all phrase for not wanting to get involved. I presume we will be hearing much more of it the next several years.
Why is that a problem? You simply request that the court subpoena records that would be dispositive of the key issue in the case. It is done all the time - does anyone think that this is the only time in history that one party to a lawsuit has tried to hide documentary evidence from the other side and/or the court?