Mechanically, it's the OP of each thread editing the "Subject" of the first post, which changes the default subject line for all replies.
Which means that this thread's title will never be changed barring some action from The Toad, since the original account associated with this thread was erased on request. That made a whole new mess in the form of the Great Disorder (a name I chose as an ad hoc thing; I'd imagine there's other names), which messes with quote links in the threads that they were active in, but I think that's a story for another time.
I know that there's at least one other active thread whose title is very unlikely to change: the word association thread. This wouldn't normally be an issue, but considering that its title has "2^15.57" in it, which ≈ 48640, that's kinda outdated now that the thread has 64154 (≈ 2^15.97) posts as of this writing. I don't know Skyrunner at all, I came here long after their time, but I assume they just left at some point.