storage conditions key
What is important is good conditions.
In hot humid situations, .22lr can go flat quickly. I know of lots of instances where guys have carried the little 5-shot .22's as deep cover guns on their persons, pockets, clipped to undergarments,armor, etc, , and found the rounds were duds after a month or so. I had the same trouble with a Berretta 21 that I carried as a third gun in a boot. So much so that I would recommend swapping out .22 ammo bi weekly if forced to carry it as a SD round under any conditions.
But, controlled environment, safe, locker, AC/Heat.....should be good for long while.