Hi,
White labels are something different. They are early pressings which are of a limited run. They appear before the record gets a general release. They are usually a promo item to promote the artists forthcoming releases or gigs. They get sent to people in the music industry such as radio & club DJs, Radio & Tv stations, shops, promotors. They are also test pressings again on a limited run & maybe to test a tune or song.
White label are usually a test bed for the forthcoming music hence the minimal packaging. In most cases it just a record with a white label in a plain sleeve. Sometimes there maybe some print or a sticker on the label or sleeve, other case they may be some writing on it.
In a number of cases, they have different stuff (song & mixes) to the general release. They can become very collectable.
After this or at the same time, you get promos. These are special releases to promote the music of the artist. These usually come with proper labels & packaging. (This packaging can be well over the top in some cases.)
Again, it is common to get different or more pieces of music on a promo. These are given, again to various people in the music industry to help promote the acts. Promo item have an unique label number which is different from the general release. A release may get a promo run from a few 10s to many 1000s. Also a release may get a number of different promos each featuring maybe different songs & mixes for different markets and different covers & extras.
You as get items with stickers on them saying 'Promotional copy only NOT FOR RESALE'. Most of these are normal releases & no different to what's on general sale. These get sent out to promote an act.
I have a few records with the 'Factory sample' sticker on them. These will be like the records with the promo stickers on them. In most cases are like the items on general sale. I do thinks these may be also test production runs for quality.
There are also acetates knocking around. These are early test pressings which are cut a material that wears out after a few plays. These are done usually to try a record out very quickly after it has been made. These are rare. DJs use them to get a tune played before anyone else.
Dean