pipe8:
Of course, it's possible that a tin here or there has "lost" its seal -- I've had this happen once, so far, out of 1,000+ tins -- but I suspect that what you're smelling is the result of your tin coming from a tobacco factory and sitting on the shelves of a tobacco retailer. You're probably not smelling the tobacco that's in the tin; you're probably smelling the tobacco and smoke that has surrounded the tin for all its life.
If you can't pry off the lid with just your fingers, odds are the seal is good. And, assuming the seal holds, the tobacco should be fine for decades.
If you're even thinking about selling your tobacco down the road, for me it absolutely has to remain in its original sealed tin. (And if you're selling on eBay, the only way you can do that is if it's in the original tin, due to eBay's restrictions on tobacco sales. That is, you're not selling the tobacco, per se; you're selling the "collectible tin.") Others here will have different takes on this, but this is mine: If you have a 20-year-old sealed tin of a blend I want, I'd pay $50-100 for that tin (maybe more), depending on what it was. If you had the same tobacco that had sat aging in a jar for 20 years, I wouldn't give you a penny for it.
Bob