From the one paper I had linked, the which has the equations for the G3UUR method, it appears to be correct.
Attached comparing the data for all thirteen Fox crystals using the G3UUR and 3dB methods. It appears there's about a 12% error between the two setups. I can believe this. Looking again at my particular Nano's clock, at 3.6865MHz where we are working, it is off by 1Hz compared with the GPS. My guess is most of the error is from my two different jigs. While I am sure I could tweak them to get the results to match, it's rather pointless. The next step would be to try and procure some sort of crystal reference standard like the one shown (aunders & Associates Reference Crystal, model 7000022).
Then again, how good does it need to be?