So in my own game, I've just recently finished refitting my survey fleet with Xb, which really feels like the second major empire milestone after setting up my CC network.
However, I realized that by the book, I have no reason to ever re-survey my home system, as all the warp points in it are known, despite the fact that if concealed warp points existed in the home system, I wouldn't know about it until scanning with Xbs.
So we came up with a little house rule after reading through the system generation table that seems roughly fair: If you rescan your home systems, the primary system (which has 3 WPs out) has a 10% chance of having a WP that would have previously been hidden. The secondary systems have a 20% chance. And of course, if you find a warp point and convert the home system into a 4 WP system, then there's only a 1% chance for each scan after that, and the secondary systems go to 10%, then 1%
Of course, using this house rule I immediately found a concealed WP in my home system, and now it appears I've generated both a galactic oddity and an NPR. So that's going to be fun.