It's surprising how many model companies get it wrong with earlier '109 canopies. Even the relatively new Airfix 1/48th scale Bf109E has a frame on the side panels of the opening canopy. Apparently, it was modelled from the RAF Museum's 'Emil' - which had it's missing canopy replaced with one from a 'Buchon', which is the same as a '109 G , with the central frame. Why the researchers don't check, and ask questions if needed, is beyond me - there's more information and photos available now, together with real aircraft, than there were 30 or 40 years ago, so there's no shortage of detailed information.