I talked to the people at Robison Outdoors last year about this. I had a few bottles of Scent Sheild Fall Blend that to me, smelled like it had turned to ammonia.

They stated that all of the Scent Shield products are synthetic, and therefore do not go bad.

I figured if it smelled bad to me, it would to a deer so I chucked them anyways.

Buy new, erase the doubt.