How far should questions or answers be edited from the original?

Question

Consider theis post: Is philosophy a science and can it prove facts like science?

1. Originally it was about the difference between eastern and western thought.
2. That got closed as too broad but after a few brief answers. Then it was changed to "Can philosophy prove facts like science" — no relation to the original.
3. And then reopened.

What happens to the answers to the original?

I ask, because this is not exactly a trivial/rhetorical question which requires us to recognize a tension.

• On the one hand, SE encourages improving over deleting posts.
• But on the other, if the improvement crosses a threshold in the spirit of sorites and Theseus, it "nonsensicalizes" earlier answers because it essentially changes the identity of the question. So:

How do we best determine what the threshold is?

Answer 1

The broad subject matter of a question shouldn't be changed, even by the OP. I think in almost every circumstance it would be better they ask a new question. However even if the broad subject matter stays the same, changing the specific question asked always risks invalidating existing answers. This is why changing the question asked should only be done rarely, in order to have the question reopened, and also why it's a really good idea that problematic questions are closed quickly before they can acquire answers.

In this specific case I guess it turned out okay because the answers to the original question have no real value and should be deleted anyway.