I know, but the birth date of the child is not material as long as it is established that he is a minor. Back then, I doubt any lawyer would ask for the BC or the marriage certificate. But, it is curious that there is no date of the marriage in the divorce decree. I have never seen that happen.
Personally, I think they got a divorce to establish a marriage - a marriage that never was.
With the only two witnesses dead, that divorce decree will stand against any DNA challengers.