Funny how people make up their own definitions. The official definition is a van conversion.
If it has the original metal body of a van, it's a B. If it's had the body cut-up or off, or is a cut-away chassis, it's a C. It's that simple. B+ is just marketing terms by the manufacturers. They can call it whatever they like, but that doesn't change the fact.
B+ models run the gambit in sizes and configuration. They go from the small end of keeping the van dimensions, but with fiberglass slab sides, all the way up to 35' long motor coaches without the cab-over bed you see on most C's. It's gotten to the point of ridiculousness on the part of manufactures and adds to the confusion of the less informed consumer.
Retaining parts of the van, like the doors, lights, etc. Is irrelevant to the definition.
But all of this is arguing about it is really silly. The only reason it is pointed out is so that people with questions can be directed to the proper sections of online forums so they have a hope of getting useful answers to their questions. Posting your C questions in the B forum is just a waste of your time in most instances, that's all.