doulton lambeth artists monograms S.D

Hi
Does anyone known this doulton lambeth artists monograms S.D?
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I do not have access to a definitive list but I have a significant number and can't find any S D or triangle with a dot marks.

There is a reference that many members of the same family decorated as production built up and I have found more than one member of the Davis family and the Durtnall family listed and both families used initials...……………. but I didn't come across an S followed by a D.

However, it is reasonable to assume that it could be another member of either of those families but, of course, it doesn't rule others out.