I hope nobody else runs into this problem, but I just found out the hard way that Photos doesn't archive libraries as does iTunes.
I installed High Sierra, updated Photos during the period I was there, and then reverted to Sierra because of a MAJOR Keychain Access bug, only to find that I could no longer open my library.
I was able to reinstall the Sierra version of Photos (Yet another MAJOR THANKS to Pacifist!), but I"m locked out of my library until I upgrade again.
Luckily, it's no big deal for me, but it could be for someone else, so the lesson to be learned is to not launch Photos in High Sierra - or, for that matter, any other macOS upgrade - until you're 100% certain that you're happy with it.
Feature request filed with Apple.
Last edited by dianne; 10/02/17 10:49 AM. Reason: Moved from Mac OS X Applications.
