I can't say I've seen an original rifle equipped with the modified rear sight. I've modified and had some spares up until a little while ago. I accumulated Mk.1 sights with smashed battle apertures and modified them myself after being instructed how to do it correctly. MoD Armourer's had a simple grinding jig which does modify the back sight slide a tiny bit for good clearance. I'd guess they were used more on the L42A1 later on.