I finally reached a TT specialist who answered in the affirmative after listening to my question just once! You're awesome, Barbie!
The answer: Don't be thrown off by TT's statement that "2017 [as of 2021] and earlier updates are not available, as these past-year versions are NO LONGER SUPPORTED." (CAPS emphasis, mine). If I need to reinstall any prior tax year version, I need only my original downloaded setup file. There's no need to save the manual patch file for each year and there is no separate state patch because the online update within the program will update the federal and all paid-for state programs.
The helpful TT specialist wanted to provide her "Employee TurboTax Specialist" comment to this post, but was unable to due to Intuit's internal departmental controls. Therefore, I'm resorting to relaying the answer and marking it as the best answer.
