I don't personally have copies Numisma but thought I'd bump this to maybe encourage someone with more knowledge to answer.
However I did see on a dealer's site the following description of the main changes in the 1994 volumes which I think are the most recent:
"NORTH, J.J.
English Hammered Coinage. Volume 1. Early Anglo-Saxon to Henry III c. A.D. 600-1272. Third edition, London, 1994. 320 pages, 20 plates, maps, lists of mints and moneyers, diagrams.
This fully revised third edition combines the considerable research and numerous finds of the past fifteen years. Included are definitive lists of the mints and moneyers of the late Anglo-Saxons, full details of the 'sceatta' series and completely revised lists of the tenth century coinage. Many new finds of the reigns of Henry I and Stephen and the Anarchy have filled the gaps in the lists along with amendments to the Short-Cross and Long-Cross coinages where all main varieties are now illustrated."
and
"NORTH, J.J. English Hammered Coinage. Volume 2. Edward I to Charles II. Third, revised edition, London, 1992. 224 pages, 11 plates.
The principal amendments to this third revised edition have been in the coinages of 1279-1351 and the provincial issues of Charles I, both of which have recently been the subject of Sylloges dealing solely with the coins of these periods. Much new information has been incorporated into the relevant sections on the strength of important studies published recently including the base shillings of Edwards VI, the milled coinage of Elizabeth I, the Tower shillings of Charles I and the mint of York of Charles I."
Hope that helps. T
.