제가 왜 이 알파벳들이 이벤트를 뜻하는 거라 의문의 여지 없이 확신한 건지..모르겠네요.

여튼....아래와 같이 바꾸는 건 어떨까요.

If an assignee was changed from A to B, then A to C, the two events will be merged into the event of which assignee was changed from A to C.