It is, in fact, true that pre-made baking mixes go bad. I generally don't use them, but I have "inherited" some from other people. I recently made one at my MIL's (mother-in-law) request. It smelled a little funny and I knew it was technically "expired". So, I added some leavening to the mix, as that's really the only thing in a mix that is going to go "bad".
I baked these oatmeal, apple muffins and they came out fine ... until I tasted them. Imagine chewing on an old piece of carpet that has been used as an ashtray - YES! It was THAT bad! So I grabbed the box from the recycling bin to check the "Use By" date; July 2010 !!!! OK, so a little past the date is fine, apparently FOUR YEARS is too much to ask, and rightfully so! Lesson learned!!
I'm sharing this with you so that you can learn from my mistake and not have to experience this unpleasantness in your own kitchen. We now return you to your regularly scheduled browsing of cat pics and song lyrics.