De-infiltrating's not part of learning to half-infiltrate, but I think it has a similar background to things that are. I know I picked up 'here's a bunch of stuff about the place you just found yourself' infodumps around the same time as I figured out de-infiltrating, and that's almost certainly part of the half-infiltration process. You have to know what's going on to sell the cover story, after all.

[Actually, the de-infiltrating knowledge was first by a few months, but Naoki promptly infiltrated on his next jaunt and didn't have the chance to test it.]