This is not true, i have been playing with the same files since 1.0...
You're wrong, and I have video evidence to prove it using your own save files from this post:
Saves are not version specific. What do you need the save for? If you want to skip the gameplay get any full save from anywhere and go to the Memories Room.
If the task still proves to be too hard for you, use this save from the discord. It's not the version you're looking for though.
Saves ARE version specific, meaning if you use an old save on a newer version of the game, some events might not trigger, because the newer version of the game might have added switches and variables that the old save doesn't have, which is the case in this situation, because Ikeda added new events and assets that where not present in previous versions. You can still use old saves and see all the content that was in available up until that point, but if you don't start a new game, you won't be seeing the content that was added later on. You need to overwrite the old save to "update" them so to speak.
Exhibit A
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You'll notice how I start a new game carrying progress from the previous saves and the event triggers immediately, but at the end when I load a save from a previous version the event won't trigger.
There are 3 reasons why the event won't trigger (this applies to all EX events a.k.a DLC):
1. You haven't met the requirements.
2. You have already seen the event (if you carry over the stats from a previous file but didn't reset the girls progress you'll only see scenes you haven't seen outside of mandatory ones like the Christmas one, new years or onsen end).
3. You are using an old save instead of starting a new file carrying progress from an old file.