It is a minefield to be too dogmatic about WW1 stuff, especially the early items, but my impression is that the Rigby marked scopes are usually essentially the Fuess Helios 3 type, or at least, nearer to the original Helios 3 than the production PPCo scopes. ('Transitional' models are sometimes encountered). I have therefore assumed that these Rigby marked scopes are early. I suspect some of them were fitted to the small number of SMLE's that were fielded with one of Rigby's own mount systems fiitted. The only surviving rifle of this type in the world that I know of is owned by a regular on this forum. I suspect Rigby fielded two (or maybe more?) mount systems though, as I have a couple of military scopes engraved to them which appear to be unadulterated, one being an Aldis & the other an ER Watts, & their mounts are identical but totally different to those on the rifle previously mentioned. I agree though, it can be very difficult deciding on these as so many were reutilised after the war & the companies involved were often H&H, Rigby, Purdey & so on, who were also involved in the WW1 contracts.