I still couldn't understand 'developers' who unable to provide compatibility of a save/load system throught releases. It's so silly and unprofessional.
And yes, I know what I'm talking about after 15 years in software development.
Well, like 90% of the software devs, with or without 15 years ... you're wrong.
Normally it's like you say, but if you USE YOUR HEAD, you'll see that almost everytime game changes the content from the beginning and it's not just adding things. This will obviously lead to missing vars/props in the save game, making it quite hard and frankly impossible to manage. They even change simple things, order of events, triggers and so. Perhaps a custom made save system would work, but it's Ren'py, so not much to customize there.
Obviously, it's annoying, but they keep improving the story, not just adding to it. The solution ? Play only every 3-4 versions, like once a year. Or wait for someone else to give you a save game. Which kinda conflicts with what I said before.
If you wanted to be right, then complain that 16.0 and 16.1 saves will not be compatible, even if 16.1 contains just bug fixes, that should not impact the save system.
Basically, I wasted 1-2h of my life, getting to the crash with the Insurance... only to have to replay everything in the next days when they release 16.1 or 16.3 or whatever. Now THIS is the issue, not what you're saying.