The LeeSpeed patent expired in 1916, so anything post WW1 is theoretically not a "LeeSpeed"
But everything on the lovely rifle speaks "LeeSpeed", the action, (Lee Metford/Long Lee-Enfield), the single shot cut off (discontinued 1916 on military rifles), sights, early (pre 1910?? safety) 5 shot mag and magazine cover are all classic Lee speed, none of which appears in the later "sporterised Lee Enfields sold after WW1

The only explanation I can think of is a pre WW1 Lee Speed built earlier but finished/proofed after WW1

Certainly better all round than mine - a Westley Richards retailed early version with full length rib and tang safety

Good luck shooting it, you will have some fun

TH44