Clients' MFJ return originally rejected because their son, who could be considered their dependent for much of the year, allegedly claimed himself.  I got a copy of his return, and he did not claim himself but instead checked the box that said "someone can claim you as a dependent."  Son got married in 2019 but filed MFS for that year.  So I went ahead and filed without claiming son. 

I know that his parents could not claim their son if he filed MFJ, but he didn't.  What am I missing?  I'd like to amend my clients' return if possible.