Distinguishing date marks on Edinburgh plate

I recently purchased a Edinburgh silver salver represented as being made in 1820 based on the date mark. But the vendor said it coudl be 1795 since she was unable to decide whether the “0” in the cartouche was for that year or the later date. The marker’s initials are “JG” . My scanner is currently out of order so I can’t send a picture, but perhaps someone on this site can help me confirm the year of manufacture. Thanks.

I think it is most likely to be 1820. I have a note of a JG mark in use around 1820, but not earlier. Here are a couple of pictures which might help you identify the year. First an example of the 1794 mark (not 1795, which is P):

and now an 1820 one:

Note the different stlye of the Edinburgh town mark and the different shape of the duty mark.

Thank you for the input. I think you are probably right. The use of essentially the same “O” in two different, with the same shield and only a bit of size difference, in relativley close years, creates some confusion…

The shape of the bottom of the shield (when clearly struck) is a useful clue. It is not just the “O” that is in question on those two date mark series, There are several letters where confusion is often seen.

In my own sampling among pieces where confusion can exist, well more than 50% of pieces I have encountered that are of the 1820 series seem to be listed with the earlier date.

Which date sequence is actually involved also influences whether a maker’s mark could be from a Glasgow maker with the piece asayed in Edinburgh. (In 1819 Glasgow opened its own assay office.)