Because the risk management plan is a live document - it will not be getting updated periodically. Plus what we have seen is now over a month old and we have not seen any risk management plan. And there will be one that it shows the mitigations that the government is telling us have been put in place or are planned for every risk in Yellowhammer.
No matter the point you release a mitigation plan it is out of date - but I still have to provide my management the current plan whenever they ask for it. I may ask for a couple of hours to refresh it if I know important things have changed - but if they want it now they get it.
The current Brexit RMP will not be very much out of date - if at all. The government's Brexit Delivery team meet daily I believe - Gove will want to see an updated RMP at that meeting.
Wouldn't part of your PM documentation be a Gantt diagram showing your mgt where you are up to with each phase and sub-phase within each task area? I wonder how each Civil Service dept tracks and reports their particular areas?
I'd be very surprised if the respective depts don't have tracking docs. How else would they themselves know where they are up at any given time and where they are against specific dates in the Gantt diagram?