Mosquito Dunks and Fungus Gnats

Hello,

Does anybody know how long an unopened pack of Mosquito Dunks are good for.
BTI ( Bacillus thuringiensis israelensis ) is the active, and I need it desperately for the gnats. I'd estimate the dunks are probably 7 years old, still sealed in the cardboard/plastic packaging. Not that I'm cheap, but I just hate to waste them, and then shlep to the garden supply shop for more.
Gnatrol changed their formula, and no longer works. BT, WITHOUT the I, doesn't cut it.
I did order a cedar/soap concoction called GoGnats, but still waiting for it.
Thanks for any help in advance.