But five years ago she was old enough to put out H-books during their tour of Nekopanda's operation, so she seemed to at least be a young adult.
Yes, but the latest remake of this eroge was 10 years ago... so to really be familiar with it you'd need to be at least old enough in 2008 to appreciate and have easy access to it. Even then, there's no shortage of eroge... it's an information glut like everything else, so you could easily miss it. Much less likely the case if you were into the scene back in 1996 when there wasn't so much of a glut and everyone was familiar with almost everything available.
As you go back in time you get a lot more universal touchstones... consider the fact that at one point everyone in the US was getting TV over the airwaves and there were three networks, so everybody from that time was familiar with practically every TV show coming out. Now, you need to follow a tonne of streaming services in addition to all the cable channels, and there's simply not even time to watch a tiny fraction of what's out there. So what you get is Gex X who grew up at a time when there wasn't really a glut and much of TV was reruns, so we got quite familiar with TV shows (and music, etc) from before we where born. This included media that wasn't exactly to our taste. But when you get to Millennials and beyond, they've always had access to more media than is possible to consume, plus the tools now to just watch the new stuff that's exactly their taste. This is really true of any generation in the info glut though... even as Gex X, I'm familiar with new material but in a much narrower band than it would be before the glut. For example, I never cared for pop music as a teen, but I'm familiar with the pop from that time because I couldn't avoid it. Now, I find it very easy to just listen to the new stuff in the genres I do care about... something which I would also have done as a teen if it had been possible.
