If an attorney represented the Plaintiff in the original action, the original judgment creditor MUST file a "Substitution of Attorney" form with the court before they can assign the judgment to you. (And until this is done, you have NO legal standing on the judgment.)
In Texas, once an "Attorney of Record" has been recorded with a court action, that attorney is the only person the court will recognize in any subsequent action, the court will not even recognize the original Plaintiff. Therefore, any assignment signed by the original judgment creditor is not valid... until they have that right by substituting themselves in place of the attorney of record.