In your example, I would think if this thread is still active after 5-6 years, it must have been a master (or even sticky) thread on the chosen topic. If it's a master thread, there must have been a wide range of discussion covered in said thread. If that's the topic of my interest, I will definitely take time to dig up all the info in such thread.

An active topic would have been very easy for any poster to spot on or locate by search. Most likely than not, it should show up either in the 1st or 2nd page in the designated forum.

Speaking for myself, as a participant in any active thread, I will rather go to one focal thread, read all the info and contribute what I have to offer or add. If I see a new thread about an existing topic that I have participated or read before, I will either post a link or RBP to the mod team so the forum mods can decide what to do. Some probably don't mind, but I prefer not to repeat myself in the new thread, if the topic has been addressed (fully or not) in the existing one. Sometimes the newer thread even becomes more active and take over the discussion. That's life, so be it.

As a reader in the fora that I frequent, sometimes I do see new threads popping up with topics that are still very fresh-inked. My first thought usually is either "Did the poster even read the forum front-page (or 2nd page)?" or "Did the poster use search before posting?"

In an ideal world, every poster will know how to search. S/he will search first then start the right thread at the right forum, if search yields no result. Our mod team won't have to encounter numerous threads with similar, if not the same, topics all the time. Sadly we don't live in an ideal world. I do feel sorry for our volunteer mods that they have to deal with this on a daily basis .

Tons of threads take their own course of life in a short period of time.

Just very recently, I saw 2-3 posters bumping threads (started in eary 2000s. I forgot which forums). No one ever posted anything since then, not until the bump. The forum mods simply closed those threads.

I haven't read that many threads but I also haven't seen a mod merge a new thread into another existing old thread that hasn't been generating any new activity for over say 12-18 months.

Besides, correct me if I am wrong, my impression is a thread with the last activity dated back to (more or less) 24-month ago is presumably dead. It shouldn't be bumped nor merged. Unless it was bumped by the OP to provide some updates or status report. In such case, I actually appreciate the poster containing herself/himself in the original thread and enjoy reading the updates.

I believe it's a case-by-case scenario since every thread has a life of its own. If the poster has any objection to the mod's action of merging thread, s/he can PM the mod and appeal the case. I doubt our mod team would mind.

Cholula, didn't a fellow FTer just win her case in the OMNI thread from being merged by you? Oops! I probably shouldn't talk about moderation in public.