He does exist with this name WO338 has him as having a TA Commission and a LG entry for his commission. But does not exist as such on Ancestry or FindMyPast or Mormons.
1895 Feb 2. . Born in Dysart, Fife, Scotland (RIC record gives 1895 in Fife, but ScotlandsPeople doe not give any Alexander G or A born Fife at that time. His marriage shows his father as John Galloway Robertson (dead iby 1919) a Sgt MAjor in Black Watch
1901 census at ?
1911 cenus ar ?
1917 Aug 1. Commissioned in Yorks LI. Alexander Galloway Allan Robertson
1920 Sep 3. Joined ADRIC with service no 484. No Coy specified.
1920 Oct 16. Resigned
1921 Dec 19. Gazetted out as Lt
1921 Marriage to Dorothea Phail as A G Robertson