WotC's steadfast refusal to publicly acknowledge the secondary resale market in any way gets comical at times, but they are a good example of how you should behave if you suspect you might have accidentally created a security.
In the case of Magic the Gathering in the 90's (the early days of MTG), Wizards of the Coast released a print run of cards the "Chronicles" set which contained reprints of cards from the earliest days of the game.
This caused a large controversy because the chronicles print run was massively larger than earlier print runs and suddenly there was an influx of cards in circulation where previously due to the limited print runs of the early sets these cards were exceptionally rare. This tanked the value of the secondary card market.
Due to the bad PR and negative attention this caused at the time WotC ended up publishing "The Reserved list" a list containing around 550 cards which they guarantee will never be reprinted.
This means for an iconic MTG card like "Black Lotus" there is a limited number of these cards in circulation and no new Black Lotuses will ever be printed.
The reserved list somewhat mollified the people that were baying for Wotc's blood at the time but now 30 years later it is more or less regarded as a mistake. There are a lot of armchair lawyers etc speculating on if they could ever renege on the reserve list and if it even represents an enforceable contract. WotC have basically refused to comment (possibly lawyers have told them not too).
