Quality of Demo LPs

Is there any difference in quality between demonstration LPs that were distributed to radio stations and commercial releases? I see a fair number of them as used records.
I have heard that DJ white promo labels are the first pressings off of the stampers, and therefore should sound better. Unfortunately, radio stations usually "kicked the crap" out of vinyl (especially by "back-queuing") so it's hit or miss as to the quality of those used vinyl LP's. The album covers usually have a "timing strip" that lists songs, running times, song intro times, and most importantly, a box that could be checked for each song, so that a program director could mark the songs that made the station's play list. Songs that had obscenities were CLEARLY MARKED so as NOT to be played. I have even seen stations that would place a little piece of those self stick labels over the offensive vinyl track, so that airplay for that song was physically impossible!

Some other goodies to look for....

There were also test pressings of single songs (usually from a new artist that the record companies were trying to promote), that were pressed onto 12" vinyl, played at 33 RPM. The album labels were blank (except for the record company name, and code number), and had a blank white jacket, with a photocopy of the artist, song title, and running time, taped to the jacket. Most of these were auditioned only ONCE, (sometimes, not even through the whole song) by the program director, and never played again, for various reasons. The fidelity of these is AWESOME!

Single songs pressed on 12" 33 RPM vinyl that were going to be the hit single of the album. These had printed labels, jackets, and timing strips, and made it to radio stations for airplay a few weeks before the completed LP was released to radio stations and to the public.

Test pressings of entire albums. Again, these had blank white labels (no song listings, but could list album title and group, and could say test printing), and came in plain white jackets, with some type of photocopied information taped to the jacket. Again, awesome sound! These are not to be confused with DJ copies, which appear identical to the finished commercial release, except for the white label on the vinyl that said, "promotional copy, not for sale".

Also look for any older LP's ('70's & '80's) pressed on Quiex 2 vinyl. Superior fidelity, and thought by many to be the best sounding of all the Quiex series!
I have generally had good success with demos, but I also passed on a few as well. My favorite of these that I have found is Dire Straits Love Over Gold.
Just avoid the ones that say "Radio Mix" or similar. These are EQed peaky for broadcast and listening on cheap radios.