These are the guides where the marketing does the most work. "Senior", "limited ingredient" and "weight control" are not defined terms — nothing stops a food carrying any of them on the front of the bag. So each guide starts with the criteria we hold the food to, then shows what clears them.
Nothing here is a medical guide. If a vet has diagnosed something, start from the condition guides instead — that's where diet is doing clinical work rather than following a preference.