Do tinned foods go off (stale)?

Assuming the can was canned properly and has not been damaged, the contents are effectively sterile, because the food is boiled in the can after it's sealed. There might be some degradation in texture and taste, but in terms of food safety, they are effectively safe.

Note that the date on your tin is given as Best Before, not Use By. That generally means it's safe to eat after the given date, but it won't be at its... best. Given that you're only 12 days out of August, and with the proviso of exercising due caution (don't eat them if they're green), you should be just fine.

Below is a direct copy of my reply to a question about expiration dates. Of course, in a sampling of old & new canned goods, they found that they preferred the old ones. (and they discussed a few foods that intentionally fermented in cans)

Lucky Peach ran an article by Harold McGee on canned goods that mentions:

Standard canned goods aren’t generally deemed age-worthy. Food technologists define shelf life not by how long it takes for food to become inedible, but how long it takes for a trained sensory panel to detect a “just noticeable difference” between newly manufactured and stored cans. There’s no consideration of whether the difference might be pleasant in its own way or even an improvement—it’s a defect by definition.

I have no idea what their standards are for storage; in the case of MREs, the shelf-life is calculated based on the storage temperature. I would assume that this would hold true for many products.

update : I just re-read the whole article I linked to, and it suggests that shelf live is temperature sensitive (and that it's used to approximate age for testing purposes):

The trouble with aging canned goods is that it takes years to get results. However, we can take a hint from manufacturers, who often accelerate shelf-life tests by storing foods at high temperatures. A general rule of thumb is that the rate of chemical reactions approximately doubles with each 20-degree rise in temperature. Store foods at 40 degrees above normal—around 100 degrees—and you can get an idea of a year’s change in just three months. But it’s possible to go further. At 120 degrees, you get a year’s worth of change in six weeks; at 140 degrees, three weeks; at 180 degrees, five days.

This is quite a common question and the simple answer is yes (within reason). Tinned food has been found that is 100 years old and still edible. For food this old, there would likely be a loss of the original taste.

As your tinned food is less than a month past its "best by" date there would be no problem in eating this. So long as food is stored around room temperature then it would be safe to eat for many years. Also make sure that the tin is not buckled or damaged in any way.

I've kept cans of beans etc for fifteen years and there still fine, if there misshapen or damaged don't use them.

I just had a tin of ambrosia rice pudding that was a whole year out of date and it was perfectly fine. Tasted and smelled normal.