What hasn't been said is: based on which tax year ?
Aren't all 2020 forms are all done.
Or will we be able to include entry in 2021 tax year to get the $$ if no check is received ?
According to the text of HR 1319, the $1400 stimulus payment is an advance tax credit against your 2021 taxes. If you have already filed your 2020 return, the IRS will guess, based on the info on that return, whether or not you are entitled to the new payment. If you have not filed your 2020 return, they will use your 2019 return to guess from.
If you do not get the stimulus now because your 2020/2019 income excludes you, or because you file on paper and your returns are still sitting in a pile of IRS mail, or for any other reason, then you will get it when you file your 2021 taxes in 2022.
This is exactly the same process as the prior stimulus payments. Everything is just moved forward one year.