MSN - A new mintmark for London?

It has been known for some time that there were two coins in existence with the mark MSN in the exergue (one in the Fitzwilliam, one from the Appleford Hoard) but, until now, it had been assumed that these were simply the result of a die engraver’s error. While completing the last letter of MSL, the engraver reverted back to the last letter of the previous MLN issue. This is much like we might write the year 2008 on a cheque during the early weeks of 2009 – a common example of the influence of previous activity. This theory does, of course, assume that these issues were in the sequence suggested by RIC.
Earlier this year, at a coin fair, I acquired an example of Licinius I with MSN in the exergue. This coin would, like a coin in the Fitzwilliam, be RIC 79 if it had MSL in the exergue. A further two coins have also come to light during my investigations.
I have now been able to compare images of four of the five MSN coins for die matches. The Appleford hoard Constantine coin is a reverse die match with the French Constantine coin. The obverses of these coins are not a match. A Waddington hoard coin, despite its poor condition, can be identified as both an obverse and a reverse die match for a French hoard example and a reverse die match with the Appleford specimen. The reverse die of these coins do not, however, match my Licinius reverse which is clearly struck from a different die. I have been unable to obtain an image of the Fitzwilliam coin as it has not been possible to locate the coin in the collections. These results are summarised in an article in the July edition of Spink's Numismatic Circular.
We have, therefore, at least two dies with MSN in the exergue, thus increasing the likelihood that this is a deliberate mintmark rather than simply a die engraver’s error. To misquote Oscar Wilde, “One die error looks like an accident, two looks like sheer carelessness, three looks like a new mintmark!” We shall await a further example with interest.