How to deal with very very old answers?

Question

There is a question How to hide users from the GDM login screen? which is 5 years old, subsequently most voted and accepted answers don't work any more.
I needed to hide a user from appearing on login screen and I found this question, I started implementing answers that are voted most and gave up after implementing 2 answers (and I believe so will most internet searchers will).
The answer that works is below with very few votes. I believe this answer should be at the top because most Linux users tend to be updated with software.

So my question how to make it easy for users to find working and less voted answers easily? Should we start a new similar question that specifies newer version and answer that works perfectly? OR do you have any idea, please discuss here.

Answer 1

Knowing that I also have quite a bunch of very old answers that dwell somewhere on this site let me suggest one thing we should always do in such a case:

Comment on the answer and tell us what was wrong.

Whenever a user is still active here they may be more than happy to get poked and may eventually adapt their answer to the different requirements of newer releases. At least they may make an edit to link to a better answer if that existed. I did so several times before.

Answer 2

1. Is the question still valid?

   If no, flag/vote to close question.

   Note, there are few situations where an old question would be no longer valid. Even in most cases when people say "I'm using 13.04, and..." the problem is still likely to exist in newer versions of Ubuntu.

2. Do you have a better answer?

   Posting a better answer is the best possible course of action, if of course you have one. The new answer will bump the question and if correct, may even get upvotes.

3. Do the answers still work on older, but still supported, versions of software?

   If yes, no course of action is needed - the answers are still valid, though you may like to add a clarifying comment saying something like "This no longer works in recent versions". Commenting like this is likely to save other people some time, and may even get the attention of the person who originally wrote the answer.

   If no, downvote the answer if you like.

   There is probably no need to flag/vote to close the answer, if the only reason it's unsuitable is that it no longer solves the problem. But if any of the flag reasons do apply, then you could flag it.