[grkvlt]

So, you're actually saying something like P(N_l = L | N_f = F) or P(N_f = F | N_l = L) is (for those sub-populations) high, while P(N_l = L, N_f = F) is still globally not common. That makes more sense, but is a different statement - the combined names are common within a local population but still uncommon globally.