Darn it. I made a mistake. When I originally measured the SNR performance of my phono stages, I used a custom-built A-weighting filter. Well, turns out I built the thing wrong. Today I rebuilt it to spec and double checked it against the chart. Now the filter is right on the money and gives me correct readings.
The good news is
that my readings were about 8dB off. I took out a Trumpet and measured residual noise at -74dB referenced to 5mV. That is "A-weighted". You can also say it's 1uV input referred noise.
Same thing with Cornet. It is now specified at 75dB SNR. That's darn good for a tubed stage.