Beautiful beautilful gun indeed.
Holland & Holland made all their .375 magnums on magnum-mausers only up around to 1920 or 1921.
The triggerguard, if one notice, is the original largebow that Mauser produced. H&H later made their own which were a little smaller and had a different profile. For me , these largebow triggerguards, witness classic Mauser from their heydays.