Given the complex variables in play, it's impossible to give a universal answer to your question. The composition of flavorings varies widely. Some are natural, most are synthetic. They will degrade, no doubt about it, but how fast, and what will they decompose in to? Multiple flavorings are often used. They interact with each other, and with the tobacco. It's impossible to predict the outcomes.
Add to this another complication: In judging aged blends, what is the reference point? Our memory is highly imperfect. How about comparing with a new sample? Well, blend compositions change, evolving as tobaccos and flavorings change or cease to be available. It's a slush puddle.
Anecdotal evidence is probably your best friend here, but we all know how reliable friends can be at times.