I'll echo the response that each tobacco type is organic and changes with the tobacco farmer source, the variations in season, changes in soil, harvesting, handling, and storage. A tin of tobacco is like a bottle of wine. I'm glad they aren't sold by vintage year, but they could be. Then given the product itself, you add all of the human variables of the smoker, the pipe, the tobacco storage, mood, mindset, and the genetics of the sense of taste, and you have a complex system. There are more variables than that, but these examples suffice to make the point. Do blends vary from tin to tin and time to time? Unavoidably.