No expert here, but the calculation I found is
CGDB - MC (Moisture Content) -.002 * 46.214
So for example
(.8073 - .04 - .002) * 46.214 ppg x 12.0 lbs = 424 gravity points (rounding), so that is a difference of 22 from your calc.
Now I have no idea which is right, but I would think CGDB - MC * 46ppg would be a good estimate and what I'm going to be using. The only thing I see wrong is not taking into account the MC. Again I'm no expert, but whoever wrote the article below seems like they might be.
BMG - Understanding Malt Analysis Sheets -- How to Become Fluent in Malt Analysis Interpretation