As with so many other things in this game, pretty much every single vet school is different on this front. Working and paying taxes in the state for a year without taking any classes (and moving your bank account, driver's license, etc.) - i.e. not being in the state for "purely educational purposes" - is a pretty common requirement it seems. But I've been a student the entire time I've been in CA, but because I'm independent of my parents, switched my driver's license, etc., I got counted as a resident at UC Berkeley after my first year of grad school and that is carrying over to UC Davis.
The same would not have played at Wisconsin, which has really stringent residency requirements. BUT, despite being generally tough about it, Wisconsin goes out of their way to say "in some circumstances you may be considered a resident of Wisconsin and another state." What I think they mean there is if you've been living out of Wisconsin but your parents still live there, they may let you slide.
Because Penn considers your parents' finances no matter your age, and because I grew up in NJ and my parents still live there, had I gone to Penn I would have argued that I should be considered a resident of NJ and applied for a contract seat - because I only ever *left* the state for "purely educational purposes."
Some schools - though not many - you can do like I did for UC and apply for resident status after your first year as a graduate (vet) student. Minnesota is one of those, though apparently most people get denied. I think Colorado and Penn are both of the type that if you're admitted as out-of-state, you're absolutely 100% considered out-of-state forever.
So yeah, depending on your exact circumstances and the schools involved, it would totally be possible to be considered a resident by two different schools. You can increase your chances of this happening by looking very carefully at the residency requirements of your two states' schools, and see if there's any way you can move just enough of your life into your new state in order to qualify there, without jeopardizing your residency in your home state.
Oh, and whether you're considered a resident by the vet school in your new state will have very little to do with whether you were considered a resident while doing pre-reqs, unless maybe you do your undergrad at the same school (or state system) that houses the vet school.
