tbac has commented on the sample rate of the larson davis 821 meter not being high enough to capture the full peaks and valleys. Lower sample rate will result in lower peak readings
LD821 has 48kHz instead of the recommended 192kHz per some obscure spec. They (TBAC) use 262kHz I think for their Silencer Summit data
All that to say, I agree your absolute measured values are probably not comparable to other published numbers by Pewscience or Silencer Summit etc
But that is a widespread issue on this topic and I am not nitpicking. Your results of side by side can testing should still stand for themselves--I preordered a 6.5 can sight unseen