GIS tools are constantly improving. This means that a yesterday accepted answer may no longer be true or at least not be the best answer today.
Should the answers' authors update them to meet the most current state of the art of the software?
I don't think it's necessarily up to the author of the original answer to update it. Many people don't return to the site after answering. However, anyone can answer a question with newer, more relevant information. Over time, that answer might get more votes than the original and float to the top. The asker may then accept it over a previously accepted answer.
I agree with @Fezter's answer and would just add that I think care should be taken to not remove answers, or information from answers, that may mean those using older versions can no longer access it.
By all means add new answers, or perhaps just update an existing answer, but always leave the question with additional useful answers rather than replacing answers that may still be useful to someone seeking an answer to the question asked using any version.