This does result in the potential for varied CP lengths depending on which route or franchise you are talking about... Though devolution to the NR routes may require this anyway.
Mick notes that he has seen cases where NR lets staff go in CP5 that it knows it will have to re-hire in CP6.
With a long-term plan, this would be identified early-doors.
Namely that they will follow a develop - design - deliver pipeline outside of the Control Periods.
@RAIL says a hearty "yes" and suggests that as an industry we have made it very hard for this seemingly hefty pile of money to end up as rails on the ground.
Hopefully this was as useful for you to read as it was for me to (albeit loosely) "live" tweet!