Hi,
Yes Sir Basset is very right in his statement.
I believe it would be a good idea to improve the British & Irish Date Letter Chards shown at our forum and to include in the Chards the correct Sterling Standards Marks, City Marks and Duty Marks in combination with the relevant year letter cycle. I realize this will be only helpful to narrow it down a little better. We always need our books and the opinion of Experts.
I found this on the net;
Irish silver offers some complications in regard to its markings, and it is especially interesting in its character.
Dublin is the centre of the silversmiths’ work in Ireland, and officially the Dublin Goldsmiths’ Company holds the exclusive right of assaying and marking Irish silver ; but, as we shall show, there was excellent silver made elsewhere in Ireland, notably at Cork, and in the section devoted to Irish silver some fine specimens are illustrated.
The Standard Mark is the harp, and was used with the crown added to it, in the year 1637, under the terms of a charter granted by Charles I to the Goldsmiths of Dublin.
In England from 1784 to 1890 the head of the sovereign was added as a mark to denote that duty had been paid. But in Ireland a Duty Mark was in force as early as 1730, viz. the figure of Hibernia. In 1807, in the reign of George III, the duty was raised ; and it was enacted by George Ill that the king’s head should be stamped as a Duty Mark. This was continued till 1890, as in England, but at the same time the old Duty Mark of the figure of Hibernia was retained, and has still been used since 1890. The figure of Hibernia may be practically regarded as a Hall Mark, although it was first adopted to denote that duty had been paid.
The Maker’s Mark, in the early days a device, and later initials, follows the practice of assay offices in England. The date letter was used from the middle, of the seventeenth century. The present series of letters from 1896 to 1920 covers the alphabet from A to Z (omitting J) in old English capitals.

Dublin. 1770. In these marks, drawn from a cream-pail, the figure of Hibernia appears. It will be noted that this is prior to the addition of a Duty Mark in England (in 1784), and prior to the further addition of a second Duty Mark in Ireland (in 1807), when the head of George III denoted that duty had been paid. The Maker of this piece was Will Haynes. The date is about 1770, but undecipherable.
For the full story see;
http://antique-trails.com/2009/hall-mar ... all-marks/" onclick="window.open(this.href);return false;"
Oel