Let's ask the question:
How many "testimonial renewals" does RRTC process in a year?
If everybody's experience is the same as mine, it's probably about 5% of the number of courses we certify in a year.
That means, for even the busiest of us, you can count the number of renewals on both hands.
If we limit the applicants for a renewal to the original measurer, and require them to produce original measurement data, my guess is that those numbers drop further.
I don't think that's much of a quality assurance issue.