There are a few names I think are being confused. Jan, short for Janice is a female name, but Jan in Central / Eastern Europe as a form of John is masculine. Jean the female name and Jean the french male name are different.
Kim is another good one - I've met several Korean men named Kim.
Though I'm not 100% sure they weren't using their family name as their everyday identity name (the Kims I met were not related).
I was going to say the same about Jean; I think that one at least is hard to really draw conclusions from without additional data like languages spoken at home.
Anecdotally, the boy->girl names are almost all very popular names where I've met multiple each of those across different ages, whereas the other two categories feel like they have a lot more down-list entries.
Going by the peak time on the chart, Jean flipped over fast right about when Jean-Luc entered public consciousness.
Yeah immigration and mix of similar names from different languages could also be reasons for the (at least perceived) shifts.