Umm, not to be rude, but why don't you try calling the Merial phone
number on the package.

A Merial customer service person told me that their flea products don't
have an expiration date and therefore don't print the dates on the
packages anymore. They also said that their flea products will be good
for several years. I'm guessing they'll be good for at least three
years. I don't know if the chemicals lose potency or not after that
time.
I really wish they'd put the expiration dates back on the packages. It
at least gives you an idea as to how old the product is when you buy
it. I just bought one a few months ago and I suspect that it's a few
years old but I have no proof of that. I do know that it isn't one of
the counterfeit versions going around, I always check that out before
using it.