Welp, Seph's been there for the past two years about, but the only people she's actually interested in finding are her mother and Hades. So... Plus they run in different circles, although I'm sure some of Seph's classmates/peers have used Zeus' papers and whatnot.

I guess what I'm saying is: it could go either way. Seph would never have used his services for anything, nor would she have sought him out herself. But they could have bumped into each other?