This phenomenon, we read occured on crowns dated 1651 thru’ 1653. Before in 1649 two different obverses are in use - one with a conventional letter N and another obverse with an inverted letter N.
Examples of crowns dated 1651 thru to 1653 are shown and none of these examples even hints that the second N in ENGLAND has been punched twice with a reorientation of a punch. So the idea that these crowns have a letter N over an inverted letter N seems a little odd. The precision on placement probably exceeds that which was possible in the 1650’s with manual techniques.
As a double check closeups were also taken of the 1654 crown and that looks as solid as the 1653 crown, letter N, although the font is different.
Below are closeups of the 1653 crown and the 1649 crown with the letter N inverted. This gives some idea of just how difficult it would have been to use the inverted N punch twice and not show any double imaging or lack of registration.
Looking for a match to the 1649 punch the closest appears to be the centre image of the 1652 date.
So does the N over inverted N exist? Probably not and if it did it would be highly exceptional and not as widespread as the suggested spread over 3 years.