Data and hypothesis – other British open-cockpit types – (Hawker Hart (IIRC) and Avro 626) sent to Canada had ‘one off’ coupe tops fitted.

The Swordfish in Canada later were famously fitted with the canopy (locally designed?) which gave rise to the mythic ‘Mk.IV’ designation.

The Canadian produced Lysanders had proper (i.e. not British) heaters fitted for the somewhat draughty cockpit.

Canadian Tigers were the ones which got the canopy, of course.

In the period blind flying instruction was carried out under canvas hoods in the Commonwealth services – I’m not aware of dedicated ‘hard top’ covers being used – anyone?

Therefore there’s no good evidence for anything else, like blind flying (good suggestion though! Evidence to prove me wrong with that statement welcome too…) and ample evidence of winterisation efforts (unsurprisingly) carried out from ad-hoc examples to mass production.

Just eddicated guesswork, of course.

Don’t forget the RCAF’s Blackburn Sharks. They were fitted with a canopy, too.