https://en.numista.com/catalogue/note312249.html
This is a scarce note.
Two dates have been recorded: 10 Nov 1915, prefix W14; and 10 apr 1919, prefix W15.
Both are pictured here: https://www.irishpapermoney.com/old-irish-bank-notes/bank-of-ireland-old/bank-of-ireland-1918/bank-of-ireland-banknotes-1918.html
Bank of Ireland £20 notes of this era were printed with one prefix per date. Thus 1917 and 1918 cannot exist for the £20 note. 1910, 1911, 1912, 1913 should be removed from the list of dates until an example is seen.
1915 will be added.