I had the splendid pleasure of going to LA Poche in St James to hear the savior of perique talk, Mark Ryan. He talked a little about the effects of the fermentation process on nicotine. First, blends that you think of as low nicotine like Virginias or orientals, probably has enough nicotine in the leaf to kill you, maybe even more than burleys. But, the acidity of the smoke inhibits it from being absorbed. But, if you ate a small amount, you might die.
Also, nicotine doesn't just evaporate, it changes into other chemical compounds. Perique doesn't have any regular nicotine in it. In fact, by itself, it doesn't have much effect on people at all. But, the nicotine that was in the burley has been trans-mutated into other chemical compounds that make the nicotine in the added leaf more absorbent.
All perique is blended with Kentucky Burley, so if you smoke it straight it's the burley that you feel.
Also, in aging a blend, the same thing is happening. The nicotine is changing into other chemical compounds over time. And, just how those new chemicals affect us is a grab bag of surprises. I've had straight Virginias with 30+ years that blow my mind with how powerful they are. And, I have had macho big burleys that have turned to pussycats. I have also had the opposite happen, and it can be serendipitous to see how age has changed this chemical.
But, all in all, I think any observant tobacconist will tell you the same. There is no one rule of thumb for what happens with age. And, this is what keeps me passionate about keeping a cellar.