How do we deal with duplicate questions where a rule change has made an old answer obsolete?

Question

So today I came across a question about booming blade, which has been closed as a duplicate of this question.

They are duplicates, but a rule change has potentially made the old answer obsolete.

A bounty has been placed on the old question to get an updated answer. In this case we are lucky that the original question was asked by an active user, who is in a position to update the accepted answer accordingly (if they wish), but what if they weren't active (or don't care)?

The accepted answer would continue to be highly upvoted, marked as accepted and incorrect.

A passer by to the site won't necessarily understand how we treat accepted answers (and the general rule about looking at votes doesn't work well with older questions and newer answers), so we are directing people to what they will probably not notice as incorrect information.

What is the correct action in this situation? We need to ensure that casual viewers, which I understand are by far the bulk of users here, can read a question and come away with the correct answer (at least that is what I assume is the point of the site!).

Answer 1

Step 1: Bounty the question.

This is one of the purposes of the bounty system - to seek new answers to old questions for one reason or another. I will leave the bounty banner up for the full week, it points out the issue that needs addressing.

At the end of the bounty period, I will award the bounty to the best, most up to date answer. This will mark it with a blue box showing 100 points for the rest of forever. Bountied answers always stood out to me more than accepted answers when I was a new user.

Step 2: Edit the accepted answer, if necessary.

I am not suggesting we just update the accepted with new information. That is up to the answer author. But, we can improve the answer without adding new content.

Instead, we should update the answer to clearly state the version of the source material it is addressing. If the author does not update their answer, we can edit the answer with a note stating that this answer reflects the source material as it was before it was errata’d. This will clear up any confusion about the answer.

Step 2 applied.

The accepted answer was not edited during the bounty period, so I have added a disclaimer in there header:

(This answer addresses booming blade and green-flame blade as they were prior to the 2020 Errata of Sword Coast Adventurer’s Guide and may no longer be applicable to the current official version of these spells)

This is a sign post to readers that the answer addresses an outdated version of the spells and preserves the authors intent. This way, the answer is not obsolete: its value is maintained as many people will likely only ever encounter the pre-Errata versions of these spells in their printed copies of Sword Coast Adventurer‘s Guide.