...some molds run much less often than others. Especially in regards to the oversize molds, there's a lot of down time in which the factory loses precious production time to facilitate manufacturing of 44mm chips compared to their 39mm counterparts.
Because of this and the relative low number of orders on the oversize molds, the 44mm molds tend to run only once every one or two years based on what I can tell. More orders on a mold generally means a mold runs more often and more frequently. This is my understanding. David can correct me on any of this, though!