A new client to me. Tiny H.O.A. Filing 1120 instead of 1120-H, because of rental/lease income from a roof cell tower. 

Lots of change over in members. Dropped ball did not file 2020. Came to me, I have filed 2020 last week. Have discovered I mistakenly checked 2020 as the final return. Now want to file 2021. With balance due.

Should I file amended from the 2020 or 2021 version of ProSeries, or does it matter? Thinking of then filing a 2021 extension to let IRS systems digest correction completely., with the 2021 balance due. Wait maybe 2 weeks.

Your counsel is appreciated.