Thanks @RRArtie for info on how you keep your backup of original filing intact and make a copy when you're doing the What-ifs. I did the same last year, had a copy that I accessed during 2021 using TT2020 to guestimate my quarterly 2021 payments. I named it with "what-if" embedded in the name so I could easily distinguish it from my e-filed data file. Then when it came time for filing this year, I had TT pick the file that had been actually filed to carry over data (just in case I messed with the original data when doing my What-ifs). I had an exception to this rule last year when I had to file an amended paper return for 2019, then I made sure to have TT pick up the amended return when starting my 2020 return. So for 2019 I had two data files and two PDFs to save.
