When a thread title is updated that change is only reflected in the first post and in any posts made after the change.
When a thread is moved, merged, or split, we can choose to retain the original title or create new ones. We will decide based on the situation and context. When you see posts in a thread with a different title it means that those mosts have been merged in from a different thread and the original title retained - in most cases it makes it easier to follow a discussion or to find "disappeared" posts.
