For a mild example of what I'm talking about, see this 5e question.
There have now been three answers (two deleted, one (currently) undeleted) pointing out that by 5th level, a Fiend patron warlock would have Fireball on their patron's Expanded Spells list and, therefore, there is no scenario in which they can have that invocation but not know fireball. This answer is incorrect, as unlike most other similar expanded spell list features (likely the common cause of confusion), warlocks do not automatically know the spells on their expanded list and therefore do not automatically know Fireball.
What should be done in scenarios like this where there's a common misunderstanding causing people to give an incorrect answer that they delete after realizing, which leads to another person with the same misunderstanding doing the same thing because they don't see the corrected mistake of the previous answerer?
In the past when dealing with common mistakes that pop up in several answers, I've left a comment on the question in hopes that answerers notice before answering, but I have no idea if that's the proper method of handling this vs. simply continuing to correct the most recent 'wrong' answer in comments when it pops up again.