Thank you for answering this question!
I paid my tax liability when I paper mailed my very late return. In addition, it took the IRS 8 months to process.
I received a CP81 notice that they have my payment and credit on account, but they don't have my return.
Instructions are to send a newly-signed return, but I also wanted to know what date to use.
Obviously, because of the likelihood of penalties continuing to accrue if I used today's current date, I'd like to submit it with the original date ... which I have proof that I sent via USPS. I paid the penalties and interest through that payment date, and even included 2 days extra in the calculation to make sure there was no trailing fees. I used an online specific penalty and interest calculator that does it to the exact penny and (at-that time_ interest rates for each week it was delinquent.
