Death record shows William Hagan died from Cardiac Failure due to pulmonary tubercolosis due to toxameia. It seems he drank contaminated milk while in the army and contracted TB.
So I suppose that means he did not die in service, but rather was discharged and then died at home?
Milk !, good grief. !!! Well I don't know what your source is for the fact that he drank the milk whilst serving in the Army, but if that was the case, and if he was also given the milk by the Army, and if that can be proven and documented, then his death would be classed as war service related and the CWGC would add him to their database of WW2 Army casualties, even if he had already been discharged from the Army at the time of his death. Anyway you have the Army number of the soldier on the commendation letter and if he is the man who died in 1946 that's all that you need to be able to successfully apply for a copy of his WW2 service record. I suspect that he may well have already been discharged, but his service record will sort that out, as for him possibly having been given the milk by the Army, it seems unlikely because if that had been the case other soldiers would have probably also become ill, but perhaps they did. Next main question, was there more than one death in Ulster in 1946 for that name.
