Another idiosyncracy of ADCs' Royal Cyphers will - as I understand it - sadly need to be addressed in the next few decades.
My understanding is that technically for all Royal ADCs - including Nurse, Doctor and Padre equivalents - HM gives and only the same HM can take away.
So - on change of Monarch to put it delicately - those who had the "big" cyphers of the previous Monarch would retain "small" ones in perpetuity, as the "awarding" Monarch is no longer around to "remove". If subsequently made ADC or equivalent by the new Monarch, they would also wear the "big" version of the new Royal Cypher.
I believe that was what was done in 1952 - I must search for photographic evidence, as there should be some in the 1950s with small GVIR and big EIIR.