I agree with bmoran4. You have to remember it was a production process for toys. Most likely there was a transition period of some length and even after the transition there would have been stock on hand for future production which would have been made using the earlier process.
If you really want to have fun with production changes try collecting pre-war American Flyer. The standard joke about collecting pre-war Flyer is in order to have all of the production variations for a particular item you would need to own every copy of that item currently in existence in the world. 
