Well Jimmie, you prompted me to take a closer look at my six examples (sad I know, but most came my way more or less accidentally) and your suggested classification seems to fit OK, but there is a complication. When was the spring shroud changed from steel to plastic? I have five examples of the G2 falling into your variant 3 category, and only one of them has the black plastic shroud. So the changeover to plastic must have occurred at quite a late date. If so, then then I wonder how your interesting steel-shrouded fourth variant fits into this timeline?

Interestingly the only first variant pistol I have is marked as ‘Milbro Mod 2’, and it happens to be nickelled. All the variant 3 examples others are marked ‘Diana Mod 2’. Is this significant I wonder? Have you found any examples of later variants that actually have the ‘Milbro’ stamping?