Cita: "ceh2019"We already split the notes at the point when specific Northern Irish versions appeared. This was in 1922 for the Belfast Banking Company and Northern Bank, and in 1929 for the other banks. The ruling authority we display for the 1922-1928 notes issued for all of Ireland is that for the Free State. It isn't perfect but to extend George V's dates in the south to 1928 wouldn't make sense either.
This was in 1922 for the Belfast Banking Company and Northern Bank, and in 1929 for the other banks.
You are correct in choosing 1922 as the split point for the Belfast Banking Company, as the Belfast Banking Company withdrew from operating in the Irish Free State promptly after partition. This resulted in 100% of its note issue being apportioned to to Northern Ireland in 1929.
However, you are mistaken in saying that the Northern Bank issues from 1922 should be apportioned to Northern Ireland - the reference you used for this is not correct.
Northern Bank currency note issues were split in 1929 along with those of the other associated banks.
SCWPM (16th Ed, p738) is correct on this in the Ireland section.
SCWPM (16th Ed, p927)is also correct in its Northern Ireland section, starting Northern Bank Northern Ireland in 1929.
Northern Bank continued to operate throughout Ireland post-partition, and its note issues were split between the Irish Free State and Northern Ireland in 1929, with 72% of its circulating notes being apportioned to Northern Ireland (as its Northern Ireland issue), and 28% to the Irish Free State (these were allocated to its Consolidated Bank Note Issue).
72% figure for Northern Bank is taken from: Moynihan, M. 'Currency and Central Banking in Ireland 1922–60', Gill & MacMillan in association with the Central Bank of Ireland., 1975. Page 160., as cited on 'The Partition of Irish Currency'
https://www.irishpapermoney.com/special-sections/Partition-of-Irish-Currency-1928-1930.html
(Moynihan was Governor of The Central Bank of Ireland, 1961-1968).
See these also:
Northern Bank 1929 overprints on earlier notes for use in Northern Ireland can were created to use up unissued note stock. These notes were issued in 1929 and form part of the Northern Ireland issue.
Northern Bank General Issue 1921-1927 £1 notes were not overprinted. Some £5 notes dated 1927 were issued as part of the all-Ireland issue, and some with 1929 overprints as part of the Northern Ireland Issue in 1929.