how long does spray paint last?

[MrTube]

I have several cans of Seymour brand stainless steel paint. Its dated November 2006. It was kept in a heated garage for 3 years. One can was used a year ago or so and I did some testing with it. After some shaking it sprayed fairly decent. I know Seymour says the shelf is only 2 years.

How can I tell if the unused cans are good? Is there anything specific to look for?