In reading numerous posts, it appears the important question and answer on the adult dependent's return is "Someone CAN claim (The adult dependent) as a dependent". Four of the 5 tests were easy, but I wasn't sure about the "Support" test. To answer this I found "Worksheet 2. Worksheet for Determining Support" in Publication 501. Filling out that worksheet truthfully, the answer to the "CAN" question is definitely YES. At that point, it does not matter if anyone actually claims the dependent or not on their return in regard to the first 2 stimulus payments. If the adult dependent CAN be claimed, the adult dependent would not get a stimulus check. It appears that amending the 2019 return would not help or be proper if the adult dependent COULD be claimed on someon'e return. For the 3rd stimulus payment, the return that does claim the adult dependent does get the stimulus payment by claiming the dependent.
