A complicated question that hopefully has a simple answer

Hello!  Last year my dad's Alzheimers became too much for him to handle his finances, but fortunately we have a power of attorney and so forth.

 

I found on taking over his finances that he was unaware of how taxes are paid on EE savings bonds he'd been holding in paper form, bringing them into the bank to cash when he needed money.  Problem was, quite a few of the bonds he'd sold and still held had already matured, and having never held paper bonds I wasn't aware that the taxes were owed in the year of maturity, not the year of sale.

 

With his help, I put the bonds into TreasuryDirect, which promptly converted the matured bonds into a "C" bond that wasn't interest bearing.

 

So I sorted out everything, and refiled his 2016/2017/2018 returns to show the correct savings bond interest income including the freshly converted ones that had matured over the last few years, paid the back taxes and the interest/penalties and then...

 

...got a 1099-INT with all of the bond interest on it that I'd already amended/refiled and paid.

 

I *presume* I put all of that into turbotax, and somewhere there's a form or something or other that deducts 1099-INT already paid in a prior year?

 

Is it also helpful to write a short letter or fill out some form explaining the mechanics of what happened?

 

I also presume I can sign his returns with the POA (which is all encompassing, every box checked) or do I need to attach the POA?  Didn't get that far yet.

 

Any help on this presumably odd occurrence is most welcome.  Thank you.