From the FWIW Files®
We are a Joyetech supplier and only carry Dekang (Changning Dekang Biotechnology Co., Ltd.) e-liquid. I'm no biochemist, but we follow their regs and keep our liquid at 40 degrees. Most of our inventory is turned in under a month, but we have (on occasion) had batches that sit in inventory for up to 120 days.
IMO - the real damage comes in shipping. Overheated warehouses, 100+ degree trucks, etc. therein lies the danger.
DIY manufacturers may hold the key to providing clean bottles of liquid, free from temperature shock, but that won't be until the FDA clears OSHA-compliant labs. Pushing to keep electronic cigarettes in the public view and away from prohibitionist bathtub gin connotation is our best defense.
Once e-cigs (and DIY liquid) goes underground, we've lost the momentum and public support.