This happens all the time. It's usual to link to the old post when it had a lot of attention. (The thresholds is not clear. 20 upvotes? 20 comments? 20 upvotes + comments? 40? ...)

An exception is when the older post has a very good comment. And in those cases I sometimes quote the comment partially.

More (less?) details in: https://news.ycombinator.com/newsfaq.html