From a novice`s point of view...who absolutely do not have any knowledge about double rifles...but read up a lot to improve my poor knowledge about classic doubles ...

The .500/465 Nitro Express introduced around 1907 is yet another large rimmed, necked round from Holland & Holland for use in their single shot and double rifles.

Like John pointed out:
The .450 No.2 Nitro Express was introduced by Eley in 1903 and was designed for use in both single shot and double rifles.

Based on the old black powder 500/450, the .500/450 Magnum Nitro Express was introduced by Holland & Holland for their single shot and double rifles during the late 1890s

The .475 No.2 is another large cartridge of the early 1900's and was available in two different loadings
.475 No.2 Eley

As mentioned before...info from webpages.( Kynoch web page)..but I really would like to build of buy these doubles when good fortune smiles on me some day...