I've seen some questions (usually in links from a question) that are, I believe, duplicates of an old question, with a different phrasing. 

Typical case: 

* [Why developers hate iframes?](https://stackoverflow.com/questions/1081315/why-developers-hate-iframes) (2008)
* [Are iframes considered 'bad practice'?](https://stackoverflow.com/questions/362730/are-iframes-considered-bad-practice) (2009)

Both questions are more than a year old, have high reputation, and have very good and enlightening answers. However, they are duplicates, in my opinion. 

Should I flag the less old one? Should I consider them as so historic that they should stay as they are?

On the one hand: 

* moderators and high reputation users capable of voting on duplicates probably have more urgent and useful things to do
* users can still find those questions in the "similar questions" column

On the other hand, the question and answers would benefit from being "merged" officially.

I don't think this edge case is covered on Meta, nor in the FAQ, so I asked.