The Jeffery round usually has a J in the headstamp; i.e., KYNOCH .475 No.2 J NITRO. I do not know if Eley's put a J in their headstamps, obviously the box would be clearly labelled to show that the rounds inside were either for the Jeffery or the other gun, but it does not automatically follow that the rounds would be similarly marked.
However, as these rounds were for double rifles, and if you used the wrong ammo it would not shoot to the expected point of impact, I suspect that the rounds would be marked. Perhaps someone on here can show us an Eley headstamp for the Jeffery cartridge.
As Eleys stopped making rifle ammunition when they were merged into Explosive Trades in about 1920, and were probably too busy with war work from 1914, your round is probably from the late Edwardian period.
Regards,
Roger.