James,
KRRC service number (R prefix) is apparently New Armies, although the three below were initially posted to 5th Battalion, so I'm not so sure. His date of entry to France (23/7/15), does match closely with 11th & 12th (Service) Battalions, but can't be confirmed, as the following proves.
As a guide:
R/7869 joined at Winchester,3/12/14. He went as a reinforcement to 2nd Battalion 2/2/15. He was from Openshaw, Manchester.
R/7870 joined at Winchester, 3/12/14. He went as a reinforcement to 1st Battalion 16/3/15. He was from Holbeck, Leeds.
R/7871 joined at Winchester 29/11/14. He went as a reinforcement to 1st Battallion 16/3/15. He was from Cork.
At least two of the above had previous military experience, which probably explains why they were shipped out so quick.
Phil