I had an idea about Equestrian lore that I can't really fit into a story and there isn't really evidence to support this as a completely legit headcanon, so that why I'm putting it here.
After thinking about Cheese Sandwich, I got the idea that each major city in Equestria generally has their own party pony to handle the celebrations big and small. I didn't watch Pinkie Pride so I don't know why he became nomadic, but I theorize that wherever he left from is a heavily populated city that would likely have more than one party pony. I was thinking that the Crystal Empire has twelve party ponies based on the "crystal celebration" G3 ponies. If anyone would like to use this "headcanon" feel free.