Thanks Ron!I know of two older models
They’ve both got plastic sliders haven’t they?
And the Kamisori style one in your lower picture was the inspiration for the Korean Sam Seong...
My one has a spring like the RG and DX but the nose is more angular and there’s a hole on the side (which you can see in my photo) where the spring is attached.
So I’d guess my model fits in between your plastic slider versions and the RG.
Next question is when did the Feather Professional shavettes and their 50mm long injector blades first appear?
Early 1970s or was it later than that?