My girlfriend has done some work in Antarctica before, she said that it wasn't uncommon to find food ten or twenty years past its use-by-date. This is kind of the next level though.
If it's pasteurized, sealed in a can and stored at room temperature there's not much to make it go bad.
The molecules that make up living things (e.g. corn or Spam) are stable at the temperatures at which those things live. If you remove the bacteria that primarily breaks things down there's not going to be much change.
It's no different than a house with 200yo timbers.
Food colouring was quite interesting, we didn't open most things. The colouring had sort of plasticised, making gooey long threads like a soft sticky bubble-gum in a greasy, oily solution.
When my grandfather passed, we found beer from the 50s and 60s (we guessed at the ages based on the designs -- it was stamped with local sports team memorabilia). We kept some of the Pittsburgh-sports team ones, in fact, and they're at my parents home on display with the rest of my fathers sports memorabilia. I also remember finding very old unopened soda bottles, though I am not sure what happened to those. Point being, I agree with you that it's probably not as rare as one might think on a first pass.
When i cleaned out an apartment in 2003 i found a pickle jar that didnt have nutrition information included in the still fully readable label. Those have been required in the US for decades...