Guess they haven't changed in the year since I stopped being their customer; customer service also never answered phones either, so don't waste your time trying that route, either.
I would like to point out that while there's obviously a massive growth in major label releases on vinyl, there's always been a big group of independent labels getting records pressed who are certainly off the SoundScan/Nielsen radar, either selling directly or through smaller distribution chains like Dischord/ CTD/ Midheaven. I doubt it makes up anywhere near the disparity, but could maybe account for a decent chunk?