I am about to file my 2020 return.  I just noticed that my mortgage company included a 1099-INT with my mortgage interest statement.  I went back and realized I missed this on my 2018 return and 2019 return, but included it in 2017 because it was a separate document at that time.  I am assuming I should go back and amend both returns.  Can someone confirm?  Also, with regards to timing:

Can I file my 2020 return now?

Can I amend and submit both the 2018 and 2019 returns at the same time (and I know they need to be submitted separately)?

And is this an acceptable justification to include on both amended returns:

I was getting ready to file my 2020 Tax return and noticed my Mortgage Company included a 1099-INT with my Mortagge Interest Statement, instead of a separate document.  Due to this, I neglected to add this as income on my 2018 and 2019 returns, so I am amending both.