How long do pins remain on sale before retired?

Aside from special event pins and limited edition pins, I am curious if pins are a certain number run and retired when they run out, or they keep making them until they seem not to sell anymore? Just wondering because most of the on rack pins I got at WDW this month were dated 2016, but some like the Sorcerers of the Magic Kingdom rack pins and mystery box pins were dated 2012, same as the Villain Comics mystery box. Also wondering because back when I went to Disneyland I got one of the first Davy Jones pins with was dated 2007, which was smooth and had a strong color, then 2 years later I got the same pin, same exact mold and date on the back but the colors were different and it didn't have the same smooth finish. So I am guessing once they design a pin they keep the date the same even if it is a newer version?