Brightside at the ben race you drop a tag in at the start... they search through and see who started..

Yet they then called me up at 8 pm as they were looking for me, A DNS'er... I had registered for the freebies yet did't race, so knowing the system just didn't put my tag in and went for a run in the mamores...

They never checked their tag system. Admittedly I should have also let them know anyway, but they also had ignored their own system they have in place.

But in a race in Germany last week we did similar to what you say.. basically a register.. and we all just called out yes.. then we set off and they knew how many had started.