I think the order of wearing was changed in 1921 with the result that War Medals went before Coronation Medals.
This information comes from the London Gazette, 22 Apr 1921, page 3184
CENTRAL CHANCERY OF THE ORDERS OF KNIGHTHOOD.
St. James's Palace, 22nd April, 1921.
The following list shows the order in which Orders, Decorations and Medals should be worn, but it in no way affects the precedence conferred by the Statutes of certain Orders upon the Members thereof:-
To be substituted for list dated 6th August, 1918.
(1) BRITISH ORDERS OF KNIGHTHOOD, ETC.
Order of the Garter.
Order of the Thistle.
Order of St. Patrick.
Order of the Bath.
Order of Merit (immediately after Knights Grand Cross of the Order of the Bath).
Order of the Star of India.
Order of St. Michael and St. George.
Order of the Indian Empire.
Order of the Crown of India.
Royal Victorian Order (Classes I, II and III).
Order of the British Empire (Classes I, II and III).
Orders of the Companions of Honour (immediately after Knights and Dames Grand Crosses of the Order of the British Empire).
Distinguished Service Order.
Royal Victorian Order (Class IV).
Order of the British Empire (Class IV).
Imperial Service Order.
Royal Victorian Order (Class V).
Order of the British Empire (Class V).
Royal Red Cross (Class I).
Distinguished Service Cross.
Distinguished Flying Cross.
Air Force Cross.
Royal Red Cross (Class II).
(3) ORDERS GIVEN ONLY IN INDIA.
Order of British India.
Indian Order of Merit (Military).
Order of St. John of Jerusalem in England.
(4) MEDALS FOR DISTINGUISHED CONDUCT, i.e., FOR GALLANTRY.
Medal for Distinguished Conduct in the Field.
Conspicuous Gallantry Medal.
Distinguished Service Medal.
Distinguished Flying Medal.
Air Force Medal.
Indian Distinguished Service Medal.
(5) WAR MEDALS (IN ORDER OF DATE).
(6) POLAR MEDALS.
Arctic Medal, 1815-1855.
Arctic Medal, 1876.
Antarctic Medal, 1901-1903.
(7) MEDALS FOR SAVING LIFE.
Constabulary Medal Ireland).
Board of Trade Medal for Saving Life at Sea.
Indian Order of Merit (Civil).
King's Police Medal.
(8 ) JUBILEE, CORONATION AND DURBAR MEDALS.
Queen Victoria's Jubilee Medal, 1887 (Gold, Silver and Bronze).
Queen Victoria's Police Jubilee Medal, 1887.
Queen Victoria's Jubilee Medal, 1897 (Gold, Silver and Bronze).
Queen Victoria's Police Jubilee Medal, 1897.
Queen Victoria's Commemoration Medal, 1900 (Ireland).
King Edward's Coronation Medal.
King Edward's Police Coronation Medal.
King Edward's Durbar Medal (Gold, Silver and Bronze).
King Edward's Police Medal, 1903 (Scotland).
King's Visit Commemoration Medal, 1903 (Ireland).
King George's Coronation Medal.
King George's Police Coronation Medal.
King's Visit Police Commemoration Medal, 1911 (Ireland).
King George's Durbar Medal (Gold, Silver and Bronze).