It was probably just Zangoose and Seviper that were swapped. I've seen and caught two Sevipers from the past week and a half, so far, but haven't seen a Zangoose since then. On the other hand, Plusle and Minun still remain in their respective regions, as Plusle is still pretty common here, and I haven't really seen any Minun around my area.
Gen 3 regionals
Did Niantic change the Gen 3 regionals? I am in N America and I caught a wild Seviper this morning.
Answers
Zangoose and Seviper have always had a rivalry. Their region rotation chasing each other but never in the same area is supposed to represent this.
On the other hand, Plusle and Minun are friends and should appear together. It would have been awesome if they could have always spawned next to each other, even when spawning off a lure or incense.
I like how when the world is arbitrarily split into 'old world' and 'new world', then Australia gets placed in 'old world' category - what the...?
I guess it is because we have one of the oldest living societies on the planet....or just because some old and no longer relevant generalising naming system just doesn't actually fit.