For a weekend warrior a big bottle of polish can be a lifetime supply! I have bottles of Menzerna SF4500, Menzerna SF1500, and HD Speed that are aging. The Menzerna products are ~6 years old the HD Speed is ~4 years old. My question is does polish expire or go bad? Do certain chemicals evaporate or break down over time? I store them inside, they still *seem* to work, and I make it a point to shake the bottles a few times a year. What's everyone's experience?