H airborne medic, yes we have his army records. He was 3456003 John Wood, originally joined the Lancs fusiliers (darwen lad) eventually went to Royal Northumberlands and then in 1942 joined the RUR. The RUR museum kindly deciphered the records for us and found him in page 41 register 22 of the army book sets. They also sent us the following info:
30 RUR 24.6.41
30 RUR 22.6.42
1 RUR 30.7.42
Infantry Reserve 10 June 44
1 RUR appointed war substantive Corporal 1/9/41
1 RUR appointed unpaid Lance-Sergeant 8.3.43
2nd Echelon 21 Army Group: appointed unpaid acting Sergeant :appointed paid acting Sergeant 5 Nov 43
2nd Echelon 21 Army Group: promoted war substantive Sergeant 3 May 44
2ND ECHELON 21 ARMY GROUP and John Wood No 3456003
Orders of Battle Second World War 1939 - 45 Vol II page 463 by Lt Col H F Joslin HMSO 1960
(5 Nov 43 is the first date of membership for John Wood No 3456003)
Campaign in NW Europe 1944-1945
21 Army Group formed in the United Kingdom 9 July 1943
The major changes in the dozens of units took place from 23 May 1944, 1 November 1944 and 15 May 1945
Conclusion:

The Army Book sets Type 358 and the emailed documents fit precisely with John Wood No 3456003 and the latter show him to be in 2nd Echelon 21 Army Group when promoted to War Substantive Sergeant on 3 May 44.

The 2nd Echelon 21 Army Group membership may have been an attachment to this higher level formation that did not take him away from the 1st Battalion Royal Ulster Rifles records in the same way as a transfer. None of this would have affected his Service Number.

This research should be on the Royal Ulster Rifles Museum computer records for some time so that an return to this complex subject should be possible at a later date.
The above in Blue is a small portion of what they sent but this is the bit which confuses whether he went in on d-day with the RUR or not.
Exactly who is the 2nd echelon 21 army group ?? I always believed it was the group as a whole which was headed by monty?? But the museum are suggesting different.