Mossberg also makes some one off models inconjuction with various individuals or organizations. Latest example is the Clint Smith, Thunder Ranch offering.
Plus on back they offered for a short period of time a Shockwave with a true breacher barrel.
Some retailers only buy the standard configuration whereas others might have 2 or 3 different configurations of the same model.
Like John said, this is nothing new for Mossberg. Whatever sells guns!
Regards