I just finished a bottle of 100mg nic that's been in the fridge for a year or more and still clear as water. It was the one bottle I kept out for DIY when I split up two liters of nic over a year ago.
I disposed of almost two liters a year or more ago that I kept at room temp. It had a light yellow tint and a musky
tobacco odor coupled with significant
throat hit. It wasn't a total loss, though. I dribbled it on quite a few fire ant mounds around my 2.5 acres. It's been quite a while now and most of the survivor ants have moved on to more amiable territory.
My replacement nic is resting comfortably at zero degrees in a box in our freezer.