Conversation is another word for “thread” which is distinguished by participants and Subject. Change any of those, and you have a new thread. I have an example conversation that erroneously contains two threads, each with the same Subject, but have different participants, and are separated in time by over 15 months. The leading message for each thread has the same non-prefixed Subject, and their subsequent messages have the same Subject prefixed by “Re:”, strong evidence that they should be separate conversations; the 15-month time gap is another strong indicator.
As long as conversations behave this way, they offer no value to me.