There really is nothing to go on here except "2nd Lt D Duncan". This man is the only one I can find who fits. In addition many of the men without Regiments on roll are Irish. I later found the 1922 press cutting which confirms it is him
1888 Jan/Mar Born Belfast
1901 census at 1 Shore Road, West Side, Duncairn Ward, Antrim
1911 census at Mayamo, Burma as a Rifleman First Battalion Royal Irish Rifles. Aged 22 and born Belfast
1914 Nov 6. Lands in France
1916 Apr 7 . The undermentioned Wt. and N.C.O.'s to be 2nd Lts. for service in the Field. R. Ir. Fus. Co. Qr.-Mr.-Serjt. David Duncan, from R. Ir. Rif.
1918 Feb 15. R. Ir. Fus.—2nd Lt. D. Duncan to take rank and precedence in his Corps and in the Army as if His appt. as 2nd Lt. bore date of 15th day of Feb. 1918.
1918 Jun 30. Royal Ir. Fus.—2nd Lt. D. Duncan resigns his commn.
1921 Jan 17. Joined ADRIC with service no 1519. Posted to N Coy
Fined 10/1 by Coy Commander
1921 Oct 2. Suspended
1921 Oct 20. Services dispensed with by Commandant
1922 Assault charge
1922 Sues Freemans for libel
1923 Gets libel compensation of £150