I've had issues with this as well.

I think that there are so many variables in storage/temperature/humidity/moon phase/mood of the universe that there can't be an accurate answer to 'how long' it will last.

I've had some CA glues last for a couple of years, left open on the bench, and then a new bottle of the same stuff goes hard in a few months.....

In any event, I always keep a new 'unopened' package of the stuff I use the most on hand, just in case. So far, the new 'unopened' packages have all been fine for at least a year without any special attention.

Buddy