pattyboy

I'm thrilled my wife just received date for interview (scheduled August 29, 2012) of AOS from F-1 student visa to Conditional Residency however, one of the documentation requests on the NOA reads as follows:
Birth Certificates for all children of this marriage, and custody papers for your children and for your spouse's children not living with you...
My current wife (non-USC)and I have no children.
My oldest two children from previous relationships are already gone (26 and 23 years old) and I also have a 13 year old who lives with his mother. The 13 year old's mother and I only dated and the relationship was and still is amicable, but we never went though a court to file the administrative paperwork with the state of Washington. All support is paid through the state DHS so there is a clear paper trail on support, however the DHS does not keep copies of the original administrative agreement (i.e. custody papers, I think, per USCIS?).
So now the crazy part: I never kept a copy of the papers and my son's mother also did not keep a copy. And the attorney we had 13 years ago draw up the paperwork (administrative agreement required by the Wash state DHS) is probably dead (he was about 80 years old and I do not even remember his name). I was active army for about 24 years and honestly, the only thing I cared about at the time was making sure the boy was well taken care of, which he was.
Now with USCIS possibly asking for custody papers (has anyone with non-custodial kids ever been through the process of sponsoring an I-485 candidate?), I'm wondering what my next course of action should be.
Any suggestions?