I'm quite curious as well. The fact that Story, Rendering, and Animations are part of those % complete numbers makes it clear that they aren't just fixing bugs and grammar mistakes. My guess (and hope) is that they are at least adding a few more endings.
This was posted 2 days ago on their Inceton Games Patreon:
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Hi!
Polish for Inside Jennifer is looking good. We have even more people working on it so it can release as soon as possible. Not only for you, but so that we can start with those new games we have mentioned.
As the matter of fact, two of the games are already in the writing process, and for the third game, we are starting with the character development and design today.
That'll be two games for Inceton Games (this site) and the other for Inceton Games NTR.