There was an article in the Australasian Coin and Banknote magazine a few years about mules which proposed the term 'hybrid' for so-called deliberate mules.
 
	I don't think there's any doubt about the obvious mules (dies from different countries or denominations and other combinations that should never have appeared together) but the rest, regardless of intent, aren't truly mules in my opinion - new designs get tried and possibly adopted; making coins is a business and it's not unreasonable to expect a new design to be gradually phased in , or possibly not and just used up to reduce waste.