1820 maker's mark I.S or S.I

Can anyone help me identify this maker please? A pair of chambersticks, London 1820 with maker’s mark I.S or S.I. I can only find a John Schofield (reg. 1778) whose make is I.S within a double-lobed punch. Did makers sometimes invert their marks relative to the other marks? Many thanks for any guidance.
Screenshot 2024-02-03 at 09.57.01

This is IS and John Schofield but the date is 1780 (no duty mark). You ask whether maker’s inverted their marks. The right question would be “Were hallmarks inverted relative to the maker’s mark?” and the answer is yes. The maker’s mark was applied before pieces were sent for assay and the hallmark was then applied by the assay office somewhere beside the maker’s mark, positioning being at the whim of the marker.

Phil

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Oh very many thanks indeed Phil. No duty mark - I didn’t notice that! And so interesting to know that the maker’s mark was applied before those of the assay office: makes sense. I’ve learned a lot now… Thanks again.
Nick Michael
Donneloye, Switzerland