First, most people looking into this wan to put the charcoal above the plant in the tube...no resin lost.
As far as resin lose in the extraction is concerned I suspect its negligible at larger scales.
Butane impurities appear to hover around 15 ppm so an ounce of BHO (produced from 12 cans - 4200 ml - of butane) would have .063 ml of impurities. A gram of charcoal can absorb 1/3 a gram of impurity. Very little cannabinoid would be lost to a gram of charcoal. I make an ounce ever 2 months and I'm tiny by Colorado standards....TINY!
Two$10 million question need answered
1) If the charcoal is above the plant, are impurities captured in the beginning washed out by the butane that flows through later?
2) do the cannabinoids "clog" the charcoal? IE is the charcoal cleaning power being used on both cannabinoids and impurities or just impurities? Are the lost cannabinoids bonded to the charcoal or is it lost because the charcoal is wet with extract? If its just wet who cares. I'll waste 1/3 of a gram if it means I'm smoking less Isoquinoline, 1,2,3,4-tetrahydro, Pyrrolidine, 1-methyl-3-2-spiro or Imidazo(1,2-b)1,2,4, triazine. IDK WTF it is but it sounds scary. At least way more scary than Mary Jane.
I am communicating with Skunk Pharm about this now.