Do I understand correctly that to amend a 2017 TurboTax file, for example, you MUST use the 2017 TurboTax program, and you cannot use the 2018 or 2019 program? If I have the original installation file, is that enough to guarantee that it will re-install on a new computer? (I.e., Intuit doesn't assume that the file was pirated from someone else, etc., and prevent you from installing a second time on a new machine.)

Thanks for any response

Yes you need to use the same year program to amend.  Yes you can install 2017 on all your computers.  You can still update the program.   

How to move to another computer.  

The programs need to be installed from the CD or download them again.  You don't need to install them unless you need to amend or open a return.

After you get the program installed the first thing to do before you open your tax return is to update the program and install any state programs you had. Then open your file. So you first might need to start a fake return to be able to download the state program (go to File-New Tax Return).

Then go to FILE -Open and find your return.  You will need the tax file ending in .tax2017 to open in the program.

 See this article on how to move your tax return to another computer…….

https://ttlc.intuit.com/community/tax-data-file/help/how-do-i-move-my-tax-data-file-to-another-compu...

How to amend 2017

https://ttlc.intuit.com/community/amending/help/how-do-i-amend-a-return-in-turbotax/00/27372

Thank You!!!