What Chuck Klosterman says in Fargo Rock City's epilogue is that the
fact that "Flat as a Pancake" is only listed as being gold (50,000) when
his own family owned three copies is simply one more piece of evidence
that before Soundscan, there was no way of knowing what did or didn't
sell.

Given the long-time and well-documented connections between record
distributors and the mob, I would guess that not even the labels knew
for sure how much of what actually sold, just what sales were reported
to them. 

Wasn't Morris Levy finally convicted for running a "cutout" scam on the
labels that he distributed?