Alex, you are exactly correct. Raflet, I had a set of mkIVbs that had lenses that looked awful. I think it was David Farnsworth who hinted that if the lenses were removed, a simple razor blade could be used to coerce the two sides apart. A good clean with lacquer thinner and the lenses can be reassembled into the frames absolutely crystal clear. I then gave it some thought and passed my ideas across Stephen Silburn and we both concluded that the original lenses were most likely laminated with a glob of nitrate dope (also known as nitrocellulose lacquer - read the label of the modern lacquers.....), with the one piece of glass slid across the other so that no air bubbles would entrain. Just give the lacquer time to dry out. Maybe even move things along a little with a bake out in a low temperature oven. The lacquer will easily dissolve in lacquer thinner for a redo if necessary. Same goes for the MkVII and MkVIII lenses (are they not identical?).
The MkIVBs that I have worn at Oshkosh do not have anything between the two glass lenses and look great and are cystal clear although I would not fly with them that way in case of a bird strike. I hit a goose (a CANADIAN GOOSE I might add and I have the DNA test results in hand to prove it) the other day at 170 knots on approach right on the windshield in from of me. The windshield wiper was broken off and the poor bugger missed getting ingested in number one by about three inches....so we had good power all the way on in. Whew. Where did the rest of the gander go? Think Sully. I just assume have proper eye protection so will only fly open cockpit with laminated tempered glass or polycarbonate lenses.