In Germany, and maybe other countries as well, the tomato cans have a 3 digit number printed on the bottom of the can. 220 for example. That's the canning date. The good ones, read Italian ones, usually also include a 2 letter code, like SA for Salerno, which indicates origin.

Obviously not a guarantee, but you can at least eliminate ones that were canned too early or too late depending on variety. Common advice is to pick the ones canned between 215 and 245 (Early August to early September) as that's the typical harvest time.