@AmeliesUncle
The difference between example 6 in pub 501 and example 7 in the regulation is that in example 6, there is no form 8332 and the custodial parent claims the child. In the regulation example 7, the custodial parent executes a form 8332 and, because the child was in custody of "the parents" for 7 months, the special rules apply and the form 8332 is valid.
More generally, I think you are probably correct after all. I found the discussion from earlier this year, where it turns out I wisely dropped out because I couldn't find a definitive statement one way or the other. The last sentence of example 6 from the regulations seems to be definitive, although I don't know why it is only in the example and not more explicitly in the main body of the regulation.
