To begin with, you're late 71 bay is considered a 72 model. No crossover is a 71.
By the time VW started producing bays, custom factory options where quite common. For example you could order a RHD bus with sliding door on either side or even both sides. There were lots of options offered by VW and the customer could choose and customise there own bus, but more often than not customers went with standard configurations.
I'd assume your bus started life as a panelvan and had side middle windows as an option. If you look at your chassis number on the m plate it will probably start with a 21 to support this assumption. You could put the details off your m plate into the decoder to find out exactly how your bus left the factory and what options wre added. Put the numbers in here. http://www.vw-mplate.com/mcode.php?plate_type=70-79&lang=EN&p" onclick="window.open(this.href);return false;
As for the Dormobile badge, it was probably convereted by Dormobile when it left the factory, thus the extra windows. Does it still have a camper fitout?
I would say it is quite a rare set up but there were many vans made like this with different configurations. Figuring out it's history can be quite rewarding. Good luck.
