Promo Pressings

Are old vinyl "promo pressings" (for D.J. use) sonically superior than their commercial counterparts, or is the only difference the white label marked "Not for Sale"?
Promo pressings are usually the best recordings. I had worked in the recording industry for 25 yrs.
No question the first promo copies are the best sound of all. Most of the time these are mint condition when found.
i collect promo pressings, among others, for reasons already noted. the more recent promos are pressed with "quiex" labels. the ones i treasure most are those with interviews between tracks. the very best "graceland" version i own was originally produced as a radio promo for the album, with narratives by paul simon between each cut (it's a 2-lp set). -kelly
Just want to strongly second Kelly's mention of Warner Bros' use of Quiex pressings. (did any other label use Quiex?)
Two recordings that blew me away sonically AND MUSICALLY, that I have on Quiex, were;
Donald Fagen: The Nightfly
Paul Simon: Hearts and Bones
Both early digitals(amazingly) from 82, 83 era. I treat those 2,on Quiex,like fine wine.I preserve those pressings for a special listening occasion. Quiex was high end right from the source. Now if I could only find a Quiex of the debut Rikki Lee Jones, or Little Feat's, Time Love's a Hero, I would, well you know!!........Frank