Why GetQueuedCompletionStatus() does not return operation type?

GetQueuedCompletionStatus() dequeue a completion notification, but it does not return what type of notification it is (e.g. Read notification, write notification).

It is my responsibility to keep track of what operations I initiate, for example when I use WSARecv(), I add a flag to the OVERLAPPED structure that indicate what operation this is (read in this case), and when I dequeue a notification, I read this flag. So does anyone knows why GetQueuedCompletionStatus() does not return the type of operation?