There are some international differences in what these phrases mean. For example, AIUI in the USA, "South Asia" means "India, Sri Lanka, Pakistan and Bangladesh" (maybe Nepal too). In other places that might be called "The Indian Subcontinent", and "south asia" might be taken more geographically.
I'm not sure whether "South-east asia" has similar non-geographic meanings. In my mind it refers to the peninsula that Cambodia, Vietnam, Thailand, etc., sit on, but that might not be true for everybody.
So, these meanings are different for different people.
I'm not sure what this means for the appropriateness of the tags, except perhaps that if they exist, the tag wikis need to be really clear.