Precious Metal Gems (PMG) revived the trading card industry by creating an exclusive color foiled parallel set that are number limited (ex. #/100 or #/10). These numbers are foil stamped to the front or back of the card depending on the set.
The lower the number, the more difficult it is to obtain in a pack and subsequently the value of those cards are higher. In rare cases, there are even PMG variants that are "1 of 1" making that card the only one of its existence in that colored parallel.
Certain collectors hold specific numbered cards more desirable than others within the same set. The first number (e.g. 1/100) is considered the "Alpha" card of that subset while the last card (e.g. 100/100), is considered the "Omega" card of that subset. These two types of cards generally value greater in auction houses or in general sales. In other cases, the card numbered 69/100 has no real title other than the perverse innuendo that some collectors have in the hobby.
The distribution ratio of these cards from manufacturers can exist anywhere from 1 per box or 1 per case (ex. 12 boxes). Back in the early 1990s, retail stores didn't always know which buyers got which cards from packs if those customers chose to open them privately. Today, there are processes in place that support buyers in knowing whether a box/case hit has been hit through real-time streaming app venues.