London class 3b pennies were issued by Nicholas of St Albans and Henry Frowick - coins of both moneyers are common.
Data taken from Churchill and Thomas (2012) Brussels Hoard publication.
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.