I think also that with makers like Sowerby, who manufactured and Registered a vast array of shapes and patterns, they may well have considered it not-unreasonable to re-use a No. - or at least some details already Registered - if they were making a new item that was similar to a previous style. Can't prove this but very good possibility. Another point is that we're speaking here of a design that - in theory - was made and Registered something like one hundred and forty years back - such pieces should show a fair amount of wear - and if not then we might question whether this piece came from a more recent mould.