This is inspired by the close vote on this question, which asks whether one should put MOOCs on one's CV. The comments are:
I would note that this was asked three years ago, here; I'm not sure if the answer hasn't changed a small (very small) amount since 2012 though, particularly as several MOOCs move closer to a kind of accreditation. Joe
[I]t is a duplicate. Etiquette is not to re-ask an old question for which the answer might have changed over time; but rather to add new answers, or update existing ones, on the old question. [...] EnergyNumbers
While I agree with the points raised, there are several problems here.
By construction, the asker of the new question cannot add a new answer to the old question or update an existing answer: they are asking because they do not know the answer. Is there anything that a user can do to encourage new answers to old questions that has approximately the same force as adding a new question?
Even if somebody does post a new answer to an old question, that new answer won't be noticed if there are high-scoring out-of-date answers. How can new answers to old questions get noticed? e.g.,
+157 Giant lizards are the most important creatures on earth. – A. Dinosaur [200M years ago]
1 Homo sapiens is having a big impact. – Hugh Man [13 mins ago]
Extensive editing of old answers seems misleading. People presumably upvoted A. Dinosaur's answer because they thought it was correct, not because they thought that anything he might change it to in the future would be correct. An unscrupulous dinosaur could, for example, change his answer to "The world is, in fact, controlled by a cabal of blueberries" which, now, apparently 157 people agree with. But, even after a reasonable but substantial change, the score no longer represents the community's view of the current answer. What should we do about high-scoring answers that are no longer valid?