This discussion has prompted me to take digital pictures of the various numeral 9’s on my own 1859’s, and I now show some of these below. The pictures were all taken at 140x magnification by sliding next coin under the microscope without changing settings. These are all decent grade coins so I don’t think that ‘flattening’ through wear will have made much difference to the measurements which I have given. I have only taken measurements of the lengths, as width measurements would have made the pictures too busy, and I think one can see the width variations without needing to have their measurements. We all knew that Gouby B has a visibly different smaller 9, so no great surprise on that one, but I think there are a couple of other interesting things:-
The 9 (top right), which has been the subject of this discussion, is indeed narrower (in itself) than the other type of 9’s. So, in addition to being the narrowest date width of all 1859’s (at 9 teeth) it could also be thought of as a ‘narrow date’ type based upon the width of the 9 itself. Note that this 9 also has other distinguishing features e.g. shape of its tail.
The surprising one for me is that I now believe that the numeral 9 on Gouby Date Style Ab is slightly different to that on Gouby Aa. In addition to the measurement difference, I think that the area within the top loop also seems more circular on Ab. You will see that I have drawn in a blue arrow to highlight a protrusion bottom right, this can be checked against the picture on MG’s website to verify that this is the exact same die which he references.
CP 1859 date varieties (michael-coins.co.uk)
P.S. My experience is that Gouby Aa is by far the most common type for 1859, and I have this morning taken measurements of several other Aa coins, all coming in at 1.62mm, albeit with varying amounts of doubled numerals. I can also show these pictures if anyone wishes to see them.