A few decades years ago there was a batch of century imports, well worn No 4 MK II and No 4 MK I that has been "sanitized" and re-serialized. These rifles, I saw 4 of them over a ten year period were late 40s PF I/II guns which had the marking removed as sell as one Longbranch. The one thing that was identical was each of the buttstocks had a metal disc inletted into the buttock, much like the trials No 1 Mk VI and No 4 Mk IV rifles.
The best I was able to track down was these were surplused out of Rhodesia around 1996 to 1998. The chai who told me that said thee came out with ex-police stocks including a bunch of 1970s Auto 5 riot shotguns. I believe the arms were used by the BSAP or its successor, though I saw speculation they were supplied by SA post embargo (1965?), pre the large shipment of ex-Portuguese G3 rifles (1976?). In any case some No4 in colonial service did have discs inletted in them.