The guideline for editing is stated as this in our editing help:
When should I edit posts?
Any time you see a post that needs improvement and are inclined to suggest an edit, you are welcome to do so. The original author of a question or answer may always edit their own post, regardless of reputation level.
Edits are expected to be substantial and to leave the post better than you found it. Common reasons for edits include:
- To fix grammar and spelling mistakes
- To clarify the meaning of the post (without changing that meaning)
- To include additional information only found in comments, so all of the information relevant to the post is contained in one place
- To correct minor mistakes or add updates as the post ages
- To add related resources or hyperlinks
One of the most solid guidelines is that second point: your editing should not be changing the meaning of a post. However, you can clarify their meaning, which extends to ironing over a small trip-up in the rules or poor usage of terminology.
So, generally minor factual corrections are OK, but if you find yourself rewriting a substantial portion of the post just to correct it, you should probably just be downvoting it. How much is a substantial portion is your responsibility to make a judgement call on.
In your case, I'm guessing that in correcting those posts, you would be changing their meaning. Use your downvote instead.