A question (which now looks like it was previously incomplete) being modified in such away that the previous answers become useless

Question

This question was posted by user 202. As can be seen from the edit history that the question was incomplete at first(though I didn't knew that till today) (the previous question was scattered all over the post (and till now it almost is).

The initial question was:

Using Bernoulli's equation, it can be shown that the water velocity depends on the height of a tank relative to the end of a hose. In reality I find a smaller hose produces a greater velocity on exit than a larger hose. What have I overlooked to cause this disagreement?

$v=\sqrt{\frac{2(\rho g h-Losses)}{\rho}}$

The OP gave a bounty of 150 reps and I therefore invested some time to answer the question as it was in original form (but I also gathered the spread out information from his/her comments,etc.) and then I discovered today that OP found that his/her original question was lacking information (which was much crucial in answering it).

But as can be seen from its current form the previously given answers have now became irrelevant (though I have modified my answer).

So what should we do now?

The dilemma is due to the fact that without this newly added information the question becomes trivial but the answers become relevant and with this information the answers become irrelevant but the scope of the question increases.

Also the OP provides most of the information in his/her answer.

Answer 1

As pointed out here and here questions should not be edited to make the current answers invalid. In this case the extra detail doesn't seem to make things too bad, but for yourself you didn't edit the question; you posted an answer. So what are some options for when, in general, you think your answer no longer applies to a changed question?

1. Do nothing

2. Don't change your answer, but at the beginning of the answer put in something that says your answer was for version "v#", for whatever version number # you were answering

3. Don't change your answer, and flag the question for a moderator to review. If they think the new edit is too disruptive to the current answers, they may choose to rollback the question to a previous version.

4. Edit your answer to fit the new question.

5. Combine 2 and 4 by making your edit fit both the old and new versions.

What you choose to do is up to you, and in general will depend on your/other's answers as well as the extent of the edit to the question.