Tom, I think that you are missing one key word in your statement about the Silver 9 tube amps:
Only a handful of people have heard OF the Silver 9 Tube Amps, let alone heard them.
The Silver 6 Tube amps are also rarely heard of or known despite there reputedly being about 50 pairs in existence and DaveS also owns a set of those.
The Silver 7 Tube Amps are the ones that the most people have heard about, have been reviewed in magazines and touted as being AMONG the best amps ever made; all 50 pairs of them. The Silver 9 Tube Amps are the rarest of all the Carver Amps as production figures for them vary from 2 to 4 pairs in total (Bob owns 1 pair, the Editor of The Absolute Sound received a pair from Bob and DaveS's pair are the only ones I have been able to document)
From what I have been able to piece together, the Silver 6 (12 tube) were rated at 300WPC, the Silver 7 (15 tube) were rated at 375WPC and the Silver 9 (20 tube) were rated at somewhere between 525 and 575WPC .
This might explain why the early Silver-7t amps were rated at 375WPC and the later ones (as well as the Silver-9t) were rated at 575WPC.
Why let facts or common sense get in the way of your opinions.