My question was prompted by this answer where the rules were unclear at the time of answering. The complete answer was now replaced with recent info from errata. The question wasn't ever changed in a way that changes what is asked.
The guidance seems to be that answers should be improved and wrong information should be removed.
In the present case I would however say that the info is not really wrong.
What is the right course of action in this case?
Complete rewrite (as was done)?
Create a new separate answer?
Add the new info but retain some or most of the original answer?