It actually seems baffling to me that Apple is stricter and more deceptive about forcing updates than most game console companies. Our iPads are specifically for medical use, and we wanted to target iOS7.
And I'm reminded of my mistake whenever I go to read in bed. The one time I turned my back on Apple, and it cost me. Just like when I was a kid and I installed that "emergency" update for iTunes 4.01 that disabled playlist sharing. Or their crippling AirPort administrator update. I had kept copies of all my ipsw files that iTunes offered, and I thought that would be enough, but, I missed the window and I had no choice but to do iOS9.
It's really sad that I now have to be more vigilant about making my own backups, because software has become so unreliable now, I never know if a version of software I'm comfortable with will become extince overnight, replaced with some crummy "upgrade". I remember when I was /excited/ by updates. Now, I have to make sure I've backed everything up first.
> I forgot my unlock pin (because I lent my iPad to someone else) and there is no way to factory reset it without also updating the OS.
You can do this from a Mac with Erase in Apple Configurator with iOS 10 or later. You always could have done it if you happened to own an Exchange or MDM server.