Final update on the H/KN mintages, James Sweeny in his book "A Numismatic History of Birmingham Mint" gives the calculated mintages of each Heaton year (which he says are "based on RM and Heaton's records, and are deemed acurate by the RM"):
1918H - 2,572,800 which gives 1918KN - 1,088,000
1919H - 4,526,034 which gives 1919KN - 683,566
by subtraction from the Coincraft combined totals.