"Bad bag" of dog food?

When a dog has GI issues one common suggestion is "maybe you got a bad bag of dog food". Although I don't doubt that this can be the case, I'm curious to hear if anyone that has experienced dog GI issues has ever confirmed that a bad bag of food was the cause of the diarrhea. And I don't mean a bad brand or a formula that doesn't suit the dog. I'm referring to situations when the dog was fine on a food generally but the current bag was spoiled, rotten, made the dog sick, etc.

Thanks for your input!