Demonstration disk?

I believe that every such complimentary or free record destined for reviewer or radio station was an early pressing because sent out earlier than retail sales release date.
I don't think I am being too simplistic thinking of these routinely representing early pressing samples.
Having listened to early and later pressings one may find the "later" sound equal or "better."
Due to manufacturing variability any particular single vinyl record may turn out to be a fine sounding example.

Thanks a lot. Always good to fill in some area that previously I had no idea was vacant!