I had always believed (and had always followed the practice) that LabVIEW needed to be installed in "chronological order". However, with the newer versions of NIPM, it is possible (and I have done it) to install LabVIEW in "reverse chronological order". I believe this works because LabVIEW places version-specific code in a version-specific folder, and libraries (including Device Drivers) are constructed to be good for a 5-year "window". So you are able to install LabVIEW 2019 after you've installed LabVIEW 2020 without uninstalling/reinstalling.
Having said that, note that there are two (2!) versions of LabVIEW 2020 -- "regular" LabVIEW, with one license, and Community Edition LabVIEW, with another. I have no idea what happens if you try to install both (shall we call them "Flavors of"?) LabVIEWs on the same Windows 10 system ...
Bob Schor
