Each officer has a pile of files they work on....so they are not sharing all files, they each have their own loads.....that's why some people receive medicals and updates before others. Each file is given a BFD when updates are received. For example, when updated documents are received, the officer will assign a BFD to your file and will open your file on that day and may choose to send the medical. Once they send out your medicals, they assign a new BFD... that's how file move from one stage to another. A BFD is a reminder for the officer to open the file, and decide whether they should proceed with asking for updates, medicals etc.
My next BFD is on Sept. 12, and if the background/security checks are in, the officer will issue the PPR. If they are not in yet, he will assign a new BFD. That's how the MP has explained it to me.