Not sure about 100 years ago, as the tins were sealed with lead or similar. I am sure I have read that the older ones, couldn't be eaten now because of the risk of lead poisoning, wrt Scott of the Antartic and his stash.
I do remember a bloke eating chicken something from a tin that he had been bought for his wedding. He promised to eat it on his golden wedding aniversary or similar. Either way it was a good 40 - 50 years old. Apparently because it was canned whilst hot, it was going to last for years.
A lot of expiry dates now adays are complete rubbish.
A lot of expiry dates are placed on items to meet certain standards IE FFD's and Cyalume light sticks, these still work after expiry but require one to meet CE regulations. I also suspect that some contractors give an expiry date to ensure the MoD places another huge order every so many years...