Indeed, threads evolve over time as the forum’s ethos and debaters change. For example, go read the first 25 messages of this thread (part 1). There you’ll find @Gadus’s cottage trip stories and @Johannes_Sippola’s matriculation exam studies. Nowadays, the coffee room mostly features quite different kinds of writings, because the thread’s culture has changed.
The title and the first message set the context, but ultimately it’s up to the debaters what the thread eventually becomes and what is ultimately written there. Sometimes the discussion veers into really wild directions and becomes so polarized that it’s more sensible to create a completely new thread. For example, the forum’s flagging thread was created because the coffee room was full of heavy bickering about flagging, and there was a desire to preserve the coffee room’s good vibe and lighter discussion culture: