Data taken from Churchill and Thomas (2012) Brussels Hoard publication.
London class 3b pennies were issued by Nicholas of St Albans and Henry Frowick - coins of both moneyers are common.
Page updated Nov 5th 2016
As previously noted, die cutters used, apparently at random, an "N" or alternatively an "H" for the letter N throughout the voided long cross series. In looking at the statistics for the 3b coins of Nicole in the Brussels Hoard it seems that usually an N alone was used - but occasionally a mix of N and H is seen.
For class 3b, almost 82% of the London/Nicole pennies use all "N"s - with the other 18% made up of 5 other combinations.
As also seen for class 3a2, for this class/moneyer combination it is clear that all Ns are commonest, followed by other types. The all H combination is the least scarce of these others.
Collectors may want to seek out 3b coins of non-NNN type.