) Go to ~/Library/Preferences/ByHost/
2) Delete the file com.apple.windowserver.XXXXXXXX... (the XXXXXX part is quite long and will be different on every machine.) This file holds the display order you've defined previously in the Displays panel of the System Preferences. (Note that any previously saved setup for the displays will be lost because of this!)
3) Reboot
4) Now – from this point forward – never reorder your monitors in the Displays panel of the System Preferences. Instead, you need to physically reorder your cables so that the right image shows up on the right projector/display.
5) Label everything and write down how the cables are plugged in to the computer, because the cable order is critical to this procedure. Any reordering of the output images should be done in software, not in the the Displays control panel.

A comment follows shortly thereafter: "@k8tefree reports ten reboots in a row with all the monitors showing up in the right order."

I don't know if anyone has tried this procedure on more recent macOS releases, but please give it a try and report here.

Best Wishes,
Mark

P.S. At this time, we do not know of a similar procedure for Windows.