There are two sources to the information, "Soldiers Died in the Great War 1914-19" and "Officers Died in the Great War 1914-19". See below.
"Soldiers Died in the Great War 1914-19" was originally published by His Majesty's Stationery Office (HMSO) in 1921.It was published in 80 parts. Most parts covered a single regiment, subdivided into its various battalions. However, some parts covered groups of units such as the cavalry, smaller infantry regiments or other corps. "Soldiers Died" covers "other ranks" of the army only, not officers. "Other ranks" includes Privates, Lance Corporals, Corporals, Sergeants and Warrant Officers. In some units of the army, the rank Driver, Gunner, Pioneer, Rifleman, Sapper or Trooper is equivalent to Private.
"Other ranks" includes non-fighting men, such as cooks, stretcher-bearers and transport drivers.
"Soldiers Died" covers deaths within the period from 4th August 1914 (the declaration of war) to 11th November 1918 (Armistice Day) and, in some but not all cases, up to 25th March 1921.
The names of 661,960 other ranks are included within "Soldiers Died". The name used by the soldier upon enlisting and in army records is given. This means that the alias appears instead of the true given name (which of course might be unknown to the army). It is a well-known fact that many men enlisted under a false name.
The regimental number shown is that in use as at the date of death.
"Officers Died in the Great War 1914-19" was originally published by HMSO in 1919. It was published as a single volume covering all officers in the cavalry, infantry and other corps. "Officers Died" covers officers only. "Officers" includes, among others, Lieutenants, 2nd Lieutenants, Captains, Majors, Lieutenant Colonels, Colonels, Brigadier Generals, Major Generals, Lieutenant Generals and Generals."Officers Died" covers deaths within the period from 4th August 1914 (the declaration of war) to 11th November 1918 (Armistice Day) and, in some but not all cases, up to 26th September 1919. The names of 41,846 officers are included within "Officers Died", although this includes some duplicates where, for example, an officer served first in the Royal Flying Corps.
These records cover deaths within the period from 4th August 1914 (the declaration of war) to 11th November 1918 (Armistice Day) and, in some but not all cases, up to 25th March 1921.