I think the yeast ages much quicker than the contects of the tin. The best before is related to the yeast. If the yeast was stored in ideal conditions (probably not the case here), then it would be OK for some time beyond the best before. When not stored in ideal conditions, best to rehydrate the yeast prior to pitching, to a) ensure that as many living cells as possible can be pitched, &/or b) to first test for yeast viability by adding some wort (or sugar) to the ready-to-pitch rehydrated yeast, and looking for activity; if none, then a fresher yeast can be used instead.
No fear for the tins!
As an aside.... I recently started rehydrating the yeast as a matter of course. Although my beers always started no problem when sprinkling, I hadn't realised the advantages of having more living yeast, particularly in the latter stages of the ferment when things get tough for the yeast due to the higher alcohol levels, thus preventing early stalls. Asuming good hygene and procedure, no reason not to rehydrate yeast, many reasons for.