How did / do they track physical album sales?

Question

So I guess nowadays with Youtube/ Spotify/ digital sales etc. it’s pretty straightforward.

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But back before all that, if “Big Music” sends 200 copies of Meteora or whatever to your local HMV, do they count that as sales, or did they wait for the HMV to let them know they’ve only sold 80 of the 200 etc.

In: 1

Answer 1

They would count the 200 as sales, but then then numbers would be adjusted down to 80 if 120 of those were returned by HMV as unsold.

Answer 2

I just listened to this in the ongoing history of new music. Up until 1991 (?) billboard just relied on reports from samplings of record stores. Estimates, not actual numbers even.