There is always a spirited discussion trying to define the differences between a Class A, Class B, and Class C. The mistake most members make is trying to pin the Class definition to the size, amenities, horsepower, gas or diesel or a whole bunch more differences.
When the RVIA created the Classes, I doubt they were thinking of overhead sleeping accommodations, how wide the motorhome might be or whether it has single or dual rear wheels. They saw 3 distinct differences in the method of construction.
The Class A starts motorhome life as a frame with wheels and a drive train.
The Class B starts motorhome life as a complete van ready to drive.
The Class C starts motorhome life similar to the Class A except it has the front portion of the cab mounted on the frame with the back cut off.
Then some motorhome builder decided to build a small Class C, but to be closer in size to the Class B. For marketing purposes, someone decided to call it a Class B+. It still is a Class C because that is the way it left the Ford, Chevy, Dodge or Mercedes factory.