Usually the black lenses have a hole for number plate illumination which makes them post war. Post war all lenses were replace for black lenses with number plate illumination, even on the taillights we now find as NOS.
A look at the M20 currently on US eBay in that rather nice post-war demobbed condition shows that many of the components which have long been regarded as 'original' and correct are often due to 'National Service'. Many of these bikes served for far longer in peacetime than their wartime careers.
