Just to clarify about the 10:00:02 start time for his London Marathon--
The Start line mats only stay active for a specified period of time, then I believe they get turned off, or just switched over to Finish line mode, if the Start and Finish are in the same place.
So if a runner arrives very late and still ends up running the course, their chip won't register at the Start line, but it will register at other mats on the course.
When this happens, the official timing system just gives them the gun time as their start time.
This happened to a guy I know. He arrived like an hour late, but still wanted to run (he's not a real serious runner) so he did. His Start time was listed as the gun time because the Start line mat was no longer active and did not register him crossing. Needless to say, his official time was quite slow as it added about an hour to his overall time.
So Dave likely never crossed the Start line at all. May have just gone directly to the Finish line and not even bothered to go to the Start line.