I need to add something else to all of this..... I'm not sure how it is in the latest public update (The last time I tried it was on the previous one, 07471) but for some wierdo reason saves made on the latest versions (And thus having stuff like Akabekos) works perfectly when loaded on older game engine versions (Such as 0723), but as u guys pointed, definetly not the other way around. Which would be the logical thing to happen.
That's actually interesting, because normally I'd expect the game to outright reject saves from "future" builds without bothering to try loading them, since the version number is baked into a save and easily accessible. Amusingly, this is exactly the point I was making about the progression gates not actually changing save files, because if the last progression gate build is fully compatible with a random build from before Derelict started adding them, it means that literally nothing in the save changed in a way that would require invalidating saves.
Which reinforces my point that it was a choice Derelict made to force players to run through the progression gates every time.
As a different note, I noticed the other day that old presets from before the breeding and preset changes actually still work in the game, despite comments to the contrary. However, they don't behave as you might expect. If you snag a neph with an old preset in the current builds, the body always uses the base shape, and things like pregnancy and body-changing traits (such as busty) don't modify that shape. Not only that, but breeding the neph results in the game reverting to what appears to be similar to the old system, with offspring using the full preset of one of the parents if applicable, or a random preset if not.
This is an interesting indicator that the data that actually changed may not be in the save file, but rather the extra data is stored in presets. I'd have to go digging in a new save to verify that, however. Color data for individual nephs has been in the save data for years, but if the format of that data changed, or if they picked up a cache of the body shape data or new material data, it would mean that attempting to load a current save in a version from before the preset update should crash the game. If it doesn't crash the game, even when looking at nephs with new presets, it means that, once again, Derelict intentionally invalidated saves that didn't technically need invalidation.