The medal card for 4334618 Cpl AN Robbins East Yorks has the written note "Oi/c Records York fwds (forwards) list of indivs (individuals) who claim to have been awarded Russian decs (decorations) and requests instructions thereon" It is dated 25 11 1920.
There is also a card for a Lieut AN Robbins of the Slavo British Legion which took part in the Russian intervention. I haven't been able (yet) to find East Yorks although the 6th Bn Yorks (Green Howards) were there and in any event, he wouldn't necessarily have to have deployed with his own battalion. The deployment was in 1918/19 so he had a bit of time to grow in experience!
Further - his number is one of the new numbers allocated to the East Yorks in 1920. I am also intrigued by the medal roll entry for 30266 Pte AN Robbins of 1st Bn East Yorks, formerly 10th Bn 57162 who is noted as still serving when the roll was issued on 8 May 1920.
However, these are simply bits of a jigsaw. You'll get the picture on the box (so to speak) if you follow KGarrad's advice as all this seems to confirm, along with your family info about serving till 1921, that his detailed docs will still be with MOD.
And then let us know please!
PS just seen your post. If the photo is good enough, post it, the medals may be identifiable.
maxD