The sticky notes by Grif, as mentioned, and I'll add the one by Mark in this forum, I'm sure are very helpful to those who read them. But as we see there are always some who don't or won't, just as they don't read the TOS when joining. Or the appeal in red at the top of the subject line to provide info re: their systems, etc.
I had good luck recently finding a help topic via advanced search (by topic, not by author). I saw my question had been asked several times, and I was glad I didn't ask it again. 
Yet I can see it can be a problem to drag up ancient posts in the help forms, especially for FAQs. Except I suspect it is a convenience for those moderators to provide a link when the question has been asked many times before. However, I think it is more understandable that a member would start a new thread as they might be desperate for help with a problem. IMO, desperation does not seem to apply to those who take time to look for long gone threads.
In off-topic forums there may those who look for posts by certain members, resurrect old posts they made under a different name, dig up aged posts that were contentious at the time to perhaps fan the embers, and even some who have a special interest in a topic and search to see if it had been discussed.
Yep, I admit I have missed the dates on those brought forward, too. Most had no current value, but a few did merit updated discussion.
Angeline
Speakeasy Moderator