That is not correct. I am a retired CPA. A tax return is not a custody document. It is a form on which you are entitled to claim exemptions for LEGAL DEPENDENTS ONLY either in your household or for whom you provide over 50% of support. A dependent can only legally be claimed on one return (absent a rare court order). Because Barry was living with and being supported by his grandparents in 1973, only they would be legally entitled to claim him as a dependent child on their tax returns, NOT Lolo and Ann.
I have seen no documentary evidence that Ann gave up child custody of Barry and at the time of her divorce from Lolo, Barry was still listed (unnamed) as a "child of the marriage over age 18" (who could only have been Barry).
Thank you for the information
All you know is what we ALL know NOW. In 1973, the woman who zero claims was his mother and the man who he claimed was his stepfather NEITHER OF THEM claimed him as a dependant. And that’s all you can know.