I got a little confused trying to follow your info but here is what I think you said/asked

Yes, If taxpayer was alive anytime in 2020 they are entitled to the stimulus money

If taxpayer did not receive the money then $0 should have been entered $0 on the RRC worksheet

If you did not enter $0 then yes you will need to amend return because IRS will not correct RRC on returns and I will look for some documentation regarding the amending part