Thank you, sir, that's very much appreciated - I'd been guessing circa 1875 so we appear to be in quite close agreement (albeit your approach is rather more reasoned).

I wholeheartedly agree that you can never have too many SxS's: I have no plans to buy an o/u, if for no other reason that space in the current cabinet is fully spoken for, but one day a 19th C example may creep in to the inevitable 2nd cabinet...