Canned food lasts forever.
This is not
quite true, although its true enough for most purposes!
Theres actually two classes of canned goods. The ones that last the longest are classed as 'shelf stable', this relates in particular to good that may become toxic during perishing, ie meats and fish. The classic shelf stable tinned meat is the 'peardrop' tin! designed to stand on the shelf in a larder.
Old tins were not completely tin coated, so they would rust. Up until the 90s it was also still legal to seal tins with lead based solder.
Essentially though, if the tin is still its proper shape, with no deep dents, no bloating etc, and with no serious rust (it needs to come off when rubbed) which could lead to perforation, the chances are the contents are still technically edible, whatever the age!
Whether they are appetizing, thats another matter! Many foods will degrade due to acidity etc and whilst technically edible, might not be the most appealing of sustinence!
Undamaged tins, kept cool, out of corrosive atmosphere, and containing a non acidic foodstuff, can and are edible a very long time after being filled. Hence the crew of a stranded sailing boat in South Georgia in '82 who survived on tins left in the abandoned Christian Salveson whaling stations from the turn of the century!
I myself am still working my way through an old stock of ration packs dated late 80s, although im annoyed that ive run out of cheese possessed.