Ian, a request for clarification.
I interpret what you are saying is that ONCE a runner goes through the CP you can pinpoint her/him to within 5 minutes at that CP. Sounds fair.
As opposed to what happens SHOULD a runner go AWOL BETWEEN CPs? Surely in that situation you can't then pinpoint them to 5 minutes? correct? You know to within 5 minutes when they went through the last CP but not where they are?
On the Trigger I bailed out after CP2 (Crowden) whilst climbing L-Edge, way before the safety of CP3 (Higher Shelf Trig) or even before the Marshals at Bleaklow Head - after getting severe cramp ascending LE. I recognised my situation and wisely retraced my steps and sought the safety of Crowden and the WMRT, rather than stumble on towards BH and Snake. But if I had stumbled on, I doubt that I would have been on any 5-minute radar until I reached BH / Snake? The Crowden Marshals were great (indeed fabulous), but were hardly anticipating my retreat within a 5-minute window.
Apologies If I have misunderstood you. Just seeking clarification.
PS, I could be wrong but from what I have read I think Wheeze is thinking/talking about trialling a more active/dynamic monitoring system / philosophy in AL/BL races? i.e. between CP?