Fur primeness consists of two basic parts. First the fur thickens as a result of the shorter days, i.e. it is not neccessarily a response to colder weather alone. Next the skin or "leather" becomes thicker to accept the added roots of the fur that have grown. When you have a pelt that is fully furred and has thick leather it is a fully "Prime" pelt. you can tell when you have the right leather because it will change from a dark "blueish" color to a milky cream or "white" on the indside of the skin. This is very obviuos in raccoons. You may have a valuable pelt even without the leather being fully primed up. I suggest you go hunt some and then skin them and observe the color of the leather.
I just realized that I said a whole lot with out answering your question directly, maybe I should run for politcal office! good Luck!