I think adding this to the target would add useful context when splitting/merging.
I often edit the first post that gets merged to say what happened, as otherwise it doesn’t always make sense next to the other posts. An automatic indication would save time.
(e.g. It starts with a repetition of the question in the root post, as if none of the other answers in the thread exist. Or it might discuss the thread it is now in as if it was a separate thread.)