You probably should have reviewed that post before submission. :)
Clearly the biofather didn't step up and defend himself with regard to child support or otherwise. His choice after he found out about the adoption. State wouldn't likely have kept track about that if mother asserted X is father.
Daughter had no legal relationship to her biofather when he died, but what she can pull over the eyes of others, who knows. It isn't as though the biofather and she couldn't have addressed an adoption overriding any concerns of legal father, even if he'd bother to make them with regard to severing his legal relationship to the adopted daughter.
"Mom re entered the daughters life 6 months ago. She re-entered the man's life 3 weeks before he was discovered dead."
I presume by "the man" you're referring to the biofather.
"So, she would've had to hide the adoption and I guess use the original birth certificate to do so."
Well, "hide" as in not mention it, sure.
"My question is, how does one get these records?"
One subpoenas the relevant custodian of a given record, presumably in connection with an estate-probate case ... as to both of these very scary (evidently) psychologically messed up women. (You do not say what heirs this deceased man has, but they're obviously the folks who have an interest in seeing to it that neither of these wenches gets anything.)
"Was it possible the adoption was reversed without the biological father knowing?"
The state wouldn't have allowed the second husband/legal father off the hook, no. The only reason it evidently did so as to the biofather is that he wasn't located and the mother evidently established to the court's satisfaction that she tried to find him or that he abandoned the family. (And, evidently, the biofather didn't care enough to keep looking for his kid. The "didn't know where she went" nonsense is an awfully lame excuse, 'cause unless she changed everyone's name and went into hiding ....