I've had some for years, and they were fine. I just got out of the habit of using them on salads, etc. because I got out of the habit of grinding them so that I'd have them ready. When I learned about FSG, I started using them for that, and noticed no problems. Then I decided to use them on food again, and they were still fine for eating, with no rancidity. (They had been stored in plastic, in a dark cupboard.)
Seeds can last for thousands of years. They've even been able to germinate seeds taken from ancient Egyptian tombs. I don't know if flax was among those, but it's an ancient plant, one of the first things humans cultivated, and was used by the Egyptians to produce linen cloth.
Baby Fine 3B, low porosity, normal density and elasticity
CGing since July 2008