I would strongly agree w/ Jay that an in-person eyeball of the course be performed by the measurer. The start/finish/turnaround needs to be accurately located, whether through finding the survey nails or measuring from the indicated landmarks (which can and do change). And it's good, although not required, to check the intermediate points as well.
If those, and/or road names, have changed, the map needs to be updated.
To sum up, is the current policy to be as follows:
A course expires after 10 years. At that time, the original measurer can apply for a new certificate. He/she can submit the original measurement data and map, or verify the course length through one ride, which must agree within 0.08% with the originally certified distance. Otherwise, a second ride must be performed, as if it was a new measurement. In all cases, a new certificate and course number will be issued.
Is this clear and acceptable to everyone?