Shown below are further images of the marks on the back of the brooch - the mystery mark is shown both ways up. Also shown are images of further marks to the pin. One of these is pretty clearly SS as for the main marks (though the photo is not so clear) and I assume to be the (unknown) maker. Of the other two tiny marks, one looks like C7, the other looks to be too weak a mark to determine.
I would welcome all views. Thank you very much.
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