How to handle incomplete answers? (as someone who knows the answer)

Question

A new question pops up on Stack Overflow and gains a little traction in the first few minutes. Two answers were posted. But both are incomplete or partly incorrect*. You know the answer. What do you do?

1. Post a third, but this time complete/correct answer (and downvote the others?!)
2. Add a comment to one of the existing answers to suggest some changes.
3. Edit one of the existing answers.
4. Do nothing and wait what happens. Maybe they're going to fix it themselves.

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*Like 50% correct

This question is about the first 30 minutes or so of a question's lifetime when things are still moving fast.

Answer 1

Not certain why you'd only do one of those things. I would:

1. Post an answer. (voting is up to you)

2. Comment on the others to point out that you are unsure about the validity of what's being stated. It's always possible that you're simply misunderstanding what they're saying.

I personally don't like editing unless it's a textual/grammatical error but answers are technically Wikis and you can edit incorrect info/add to them but I've never felt OK with it myself.

Plus, if you're adding a significant amount of info and doing a lot of work, you should get the rep yourself rather than rewarding someone who writes answers with incorrect/incomplete content.

I would avoid using your answer to say that other answers are incorrect. It can sound combative and be "not nice". Use the comments for that and, hopefully, they'll correct their answer or explain it more thoroughly.