2023-21, it seems like the due date for an amendment is 2019 is not 7/15/2023 if your files before 7/05/2020. But rather 3 years after filing or 4/15/2020 whichever is later(assuming mo extension). So the “postponement” was more like an extension?
Amendments can generally be done at any time for any tax year. However, as a general rule of thumb, e-filing amendments can go as far back as 3 years. Anything further back than that in the past will need to be paper filed.
IRS e-file system supports current tax year and the 2 prior tax years of e-filing. Paper filing can be done for amendments further into the past. Keep in mind though that anything further than 3 years will not be eligible for a refund.
I don't think that's true. The IRS put out a notice earlier this year saying that you had a postponement to 7/15(or 17 because of the Saturday), but if you filed after 4/15, you still needed to file 3 years after the original. So if you filed on 6/22/2020, then you would need to amend by 6/22/2023. So it was like an extension and not a change of the official date.