HDR - Reservoir ???????????

Mornin all
How does the information announced on Ching 2 equate to reality? for instance.
On the 30th of July announcement on the HDR site it was stated that the Reservoir sands would be cored.
Then yesterday's announcment stated that a core had been taken from 2385m to 2348m, is this the reservoir sands? if so does that then mean that given the total depth of 2840 the potential depth of the reservoir could be 470 metres, I hope so but don't think so, can anyone explain?
Also how do they know exactly when to take the core sample, surely there must be some kind of indicator alerting them, wire lines? or examination of drilling rubble?
As Pauline Hanson would say, please explain.
regards