I suppose that a FOIA request could get the Dunhams 1973 tax return. It is not something that I personally am motivated to do.
If the Dunhams claimed Barry as a dependent because he was living with them and/or they were providing over 50% of his support and his mother was not claiming him, it would still not prove who had legal custody of him or what his nationalities he had. Claiming a person as a dependent has nothing to do with custody or nationality.
The reason i asked about those dates was because of the “anna” theory on post 11076- to see if another dependent would be listed other than stanley ann