Just to be safe, it's a good idea to smell the bottle before you drink it, especially after you've had it a while. Flax will last a good long time; some even freeze it. But once it's gone bad, I guarantee you'll know.
If I buy more than one bottle at a time I put the extras in the freezer. Yes it can go bad - - but I heard it will smell bad if it does. So follow your nose. . . . .
I just store mine in the freezer all the time. It obviously doesn't actually freeze, but just becomes a bit thicker. It is totally drinkable straight from the freezer though.