There are "SPECIAL" pins that are VERY LIMITED in the number that Disney creates.
Over the last 10 years I have been lucky enough to attend several PIN EVENTS at EPCOT - Walt Disney World.
These events are 3 day affairs that give pin collectors several opportunities to have pin collecting and trading experiences that you would not get just visiting the parks. These events offer opportunities to purchase very limited edition pins that are made just for this annual event. They also offer the ability to trade with other collectors from all over the world (California, Japan, China, etc.). I have made some great friendships due to all the nice people that you meet at these events.
Last, these events hold an auction of exclusive pins. These pins range from proof sets of limited editions to One-of-A-Kind pins. I was able to successfully bid on one of these "One-of-A-Kind" pins. It was a prototype pin from Labor Day 2001. It has all of the Disney Villans on the pin. Disney made this pin with a purple background but the one I have has a gold background. It is the only one that Disney ever made of this pin.
Wow, sounds like those are some neat events to go to. Glad you were able to snag a good set.