Are Promo-DJ Copy stamped vinyl better?


I've always wondered if a record stamped "For Promo Only" or "DJ Copies - Not for Sale" were more likely first edition/early stamps. Most of the ones I've have sounded just fine but I was wondering what those of you who worked in the music, radio, and related industry might tell us about the pressings with these stamps.
jwong
Promos tended to be---but weren't always---early in the run of pressings. So better quality is a possibility.
Stamped ones are just probably earlier in the pressing run, and have no extra value. If they have a "Quiex II" sticker then they are rather special, as they are pressed on special, better Vinyl. You can tell if it is really still a Quiex II LP in the sleeve by holding the LP up to the light: Quiex II vinyl is always slightly transparent. I have unfortunately seen some covers marked Quiex II with ordinary vinyl inside.. So you actually have to check the vinyl. Quiex II is worth a premium over the regular LP.
The other great promos are where the LP label has a special label made just for promo copies. These are usually older LPs.. and collectors rate these as also worth more than a regular pressing. The final super special promo is when the LP is a different color, only for that promo. Those are rarer still. And finally, special records never released except as promos.. the record price guides often list those as being worth thousands...