The Numista catalog currently lists all dates of this type as having a "mint letter" of R. (So does Krause.)
https://en.numista.com/catalogue/pieces146248.html
The coins have an N above the shield, to indicate Nuremberg. Below the shield, the initial of the mintmaster appears. Schon indicates that the mintmaster was Johann Martin Forster for 1760-64, and it was Georg Nikolaus Riedner for 1764-93.
The initial should be F for 1760-63.
Photos of 1764 have an R below the shield; but there may also be F coins as well.
In any event, the R at 1760 and 1763 should be changed to F.
The photo below (which is upside down) is of my 1760.
http://www.elfreeman2.com/t18/6ddd36o.jpg
