All panel vans were originally "panelled" and windows added to order if desired. A good percentage were fitted by dealers (or dealer arranged) and the aftermarket (such as Canopy Industries and others). There is genuine Holden side glass and aftermarket branded glass. Typically if a single glass is added it is passenger front (if you think 4 window side glass per panel van) and this is the one added for visibility. There was also single full length glass from the aftermarket.

None of the above were "Sandman" specific and Holden did deliver good numbers of panel vans (HJ-on) with glass fitted to dealers as stock options and from what I have learnt all appeared to be 4 window fitment.