2019 Amended Return Questions

Hello, I need to file an amended return for 2019. I filed a 2019 married filing jointly return (Federal and State) in late March 2020 and I am the primary filer. My wife inherited several investment and retirement accounts from her mother who passed away in late 2019, and I was not aware the account setup until in early December 2020 (this month). I did not get my wife's 1099 forms from the brokerage firm, where my wife has the inherited accounts, until early December 2020. The 1099 forms included a 1099-DIV with about $1,700 in dividends (about $1,200 are qualified dividends) and $70 capital gain distribution; and a 1099-B with a loss of about $80 from stock sales. This was in the period between her mother's date of death in mid-November 2019 and 12/31/2019.

My questions are:

1. I am the primary filer and my wife is the "spouse". Since we filed a married filing jointly return, would I need to include my wife's 1099-DIV and 1099-B income and loss in our tax return? If so, I'll need to do an amended return for both Federal and State, even the accounts are in my wife's name and she is not the primary filer?

2. Do I need to attach the missing 1099s to the Federal amended return? There are no federal and state taxes withholdings for these 1099s.

3. Does IRS match the 1099 records for non-primary filer ('spouse") for married filing jointly return, and at some point, I would get a notice if I don't amend the return? I am willing to pay the additional taxes, but I just prefer not to re-do (amend) the returns because of the additional time and paperwork.

4. If I do an amended return, will it create a red flag for future returns? Some web-sites say to be careful to do amendment and not to do one if not needed. I am not sure why they say that.

5. I am using the TurboTax software to do the amended returns to calculate the additional taxes, but I don't see the interest and potential penalty on the Federal 1040X or 1040SR, and the State (Michigan) amended return forms generated by the TurboTax software. Both the Federal and State instructions talk about interest and penalty for late payments, but I don't know whether the instructions are for both the original returns and amended returns. I filed before the deadline and had refunds for both Federal and State. The tax payments now are due to the missing 1099 forms. If they were included in the original Federal and State returns, we still would have not owed anything and would have gotten refunds for both Federal and State. There would be tax payments now since we got the refunds for the original returns earlier this year. Since neither the Federal nor State amended tax return forms generated by TurboTax show interests and penalties, what should I do? How would I calculate and pay the interests and/or penalties in addition to the additional taxes due to the missing 1099s that I did not include when I filed the original returns?

6. The original federal return had a refund of about $1,500 and we received about $20 more than that amount in July 2020. I assume the $20 was the interest that IRS paid due to late processing of the refund? Do I include the $20 in column A of 1040X (the numbers in the original tax return) as "adjusted”? The 1040X instructions appear to say not to include interests.

7. Does it matter if I file the amended return after the end of the year 2020? Would the interest or penalty be higher if I don’t file before the end of this year?

Thank you very much for your replies in advance.