Fermcaps not working

Does anyone know the shelf life of fermcaps? I used it two months ago and it was great. Boiled a little over 7 gallons in my 7.5 pot no problem. Today it didn't have any effect. I Probably added twice the recommended amount before I gave up. I kept it in the fridge like I've seen recommended.

 

I really don't think there is a limit. It is inert.

My bottle is over a year old and did just fine yesterday.

 

Weird. I had my pot about half full heating up and left it too long and had it boil over, so i put in a few drops and nothing happened. Then I dumped in the rest of the wort (leaving 4 or 5 inches of head space) added the correct amount of drops, brought to a boil, and almost had it go over. I added a few more drops then ended up watching it closely for the whole hour turning the heat down and stirring when it foamed up too high. Does something happen if you add it post boil?