As it turns out there was indeed a bug that caused a ton of things to unlock at 500 girls recruited. This was due to an arbitrary number being set at the very beginning of Campus Life. I'm going to keep investigating further into this with the players that found themselves affected by this. I'm not able to speak regarding other players' games but I did want to mention this publicly so that we can clear a few names up here.
As I said before, I have been wrong before and this case is not particularly different. That being said I will be working towards trying to monitor this issue to make sure the fix we put in works.