Has anyone ever had a batch of Tylenol PM that didn't seem to work?

I have had sleeping problems for years. I finally found a combination that really worked. I would take one Tylenol PM and one Melatonin 3 right at bed time. I was out, I would get 7 hours of great sleep. The tylenol bottle ran out, I bought another bottle, now doing the same exact routine with the new batch, I'm up all night again. So I was wondering if anybody else has ever got a batch of tylenol that seemed to be a dud? It seems silly but old bottle= sleep, new bottle= counting 4000 sheep.