When you move to another state, typically, in order to establish residency, you must give up your residency in your old state. For example, I moved from FL to GA. When I moved to GA, in order to establish my residency, I had to turn in my FL driver's licence and get my GA driver's license, change my car registration, prove that I am living somewhere and using utilities, etc. Last summer, I had to move back to FL and needed to change everything back. When I went to apply to dental school for fall 2016, GRU no longer considered me a resident because I will have lived in FL for a year prior to the start of classes.
Plus different schools will have different requirements for what is considered to be "in-state".