The way the VOSA testers have to work is the 'literal' meaning of the criteria in the Manual.
I looked at the section on glass and it says that if glass is fitted then it must comply with the spec; it also says that if the side screen/glass is there it must be fitted and therefore will need to comply. It makes no requirement for there to be side windows fitted. "1.
Windscreens, windows and side-screens where fitted must be securely attached to the vehicle."
If there are no obvious screw holes and no window it follows there is no glass to comply. I had questions like this with SVA and I found the VOSA head office very reasonable and helpful, it may be worth an enquiry on the lines "are side windows compulsory?" There are many '7' and 'Atom' types that have no side windows and they pass.