Sometimes, not that rarely, rules change in RPGs. Answers that were good become objectively, definitely wrong overnight, through no fault of their writer.
The accepted course of action is to do nothing, hoping that the previous voters realize the change in the facts, and modify their votes accordingly.
However, they do not. Either they do not know there was an errata, and even if they do, you can not expect people to follow all their votes, for ever. And if they do, they might not change their votes, because of the time constraint ("Your vote is locked unless the answer is edited"). The right answer for this question has only 4 votes, 10 less than the wrong one. Half a year has passed since the errata, so our approach of waiting for the problem to fix itself clearly does not work.
Someone who is unaware of the errata gets the wrong answer, which is against the intentions of this site.
Update after a week: The votes are now 11 to the right answer, 9 to the old one, very far from convincing.
How can we fix this?
I see 6 options:
- Downvote the old answer, upvote the new one, comment on old one
- Pros: Does not offend anyone, moves things in the right direction, takes small effort
- Cons: I just demonstrated that it failed to give the expected result even after 7 months
- Create a meta question about it
- Pros: Does not offend anyone, moves things in the right direction
- Cons: I just demonstrated that it failed to give the expected result even after a week, also quite high effort (I planned doing this question for a month)
- Cons: Invisible for a casual user, who just wanted to find the right answer for the original question
- Completely rewrite the old answer to reflect the new ruling
- Pros: Now the highest rated answer is also the best one
- Cons: Against current rules, more importantly could start editing wars
- Edit the old answer, add "obsoleted by rules change" as first line
- Pros: Low effort, highly visible
- Cons: The writer of the answer could delete it
- Use the flag "in need of moderator intervention"
- Pros: Low effort, highly visible
- Cons: Not immediatel clear why it was flagged
- Create new flag "obsoleted by rules change"
- Pros: Low effort, highly visible, and clear
- Cons: Might not be technically feasible
I would suggest option 4 or 6.