you may not have used the last-month rule (LMR) in 2020 because it seems both were covered by a HDHP for every month of 2020. the LMR is only used when there is a gap in HDHP coverage but there is HDHP coverage, in your situation, for the taxpayer and spouse on 12/1/20
the 2021 contribution is fine $3600 for family HDHP coverage for 6 months + 6/12 of the $1,000 catch up for him or $500
if you did something wrong on the 2020 return to indicate use of LMR, that will roll over to 2021 and
