Understand what the date is really telling you
A best-before date marks how long the maker expects the food to stay at its best quality when stored as directed; it is not a promise that the food turns dangerous the next morning. That cuts both ways. Food a short time past the date, kept sealed in a cool, dry pantry, may still smell and look normal, while food well within date can spoil early if the bag was left open in a warm, damp room. So use the date as your prompt to inspect carefully, not as the whole decision, and be stricter with wet food and opened food than with a sealed dry bag.
Inspect it like you would your own pantry food
Pour a little into a clean bowl and look before you serve. Check for mould spots, clumping that was not there before, fine webbing, pantry insects, or droppings, and check the bag itself for tears, swelling, or a broken seal that let air and moisture in. Then smell it properly: dry food that has turned usually smells sour, sharp, paint-like, or simply stale in a way that is clearly different from its normal smell, because the fats coating the kibble oxidise over time. Run a few pieces between your fingers; a greasy or sticky film that feels heavier than usual is another rancid clue. Any one of those signs ends the assessment — bin the food, do not pick out the good-looking pieces.
Weigh up storage history and how far past it is
Think back over how this bag actually lived. Was it decanted into an open container, stored near a cooker or a sunny wall, or kept through a humid spell with the top rolled loosely? Heat, light, air, and moisture all shorten a food's useful life far faster than the printed date assumes. A sealed bag a few weeks past its date from a cool cupboard is a very different case from an opened bag months past its date that has been open to kitchen air the whole time. If you cannot reconstruct how it was stored, or you are feeding a puppy, a senior dog, or a dog with a sensitive stomach or a weakened immune system, err toward throwing it out; the saving is small and the vulnerable dog carries the risk.
If you serve it, watch — and record what you served
For food that passes every check, serve a normal portion rather than a double helping, and watch the next day or so for vomiting, loose stools, unusual wind, itching, or a dog who suddenly refuses a food he normally eats; any of those means stop, discard the rest, and call your vet if the signs persist, worsen, or involve repeated vomiting or lethargy. Write down the product, the best-before date, and the day you opened and served it where the household keeps feeding notes, so if your dog is unwell later there is no guessing about which bag was involved. KinsLe's Care Teams can carry that batch note inside your dog's feeding duties, timestamped when a meal is marked done, so a partner or sitter never serves from a bag you had already decided to question.