That's a beautiful sideboard. I'm guessing that a photo of the back is not an option due to it's size. If these are all from the same matching set, can you post the underside of a chair or the table, so that we can get a look at the construction techniques used? A lot of times it is easier to get a feel for the age if you can see how a piece was made, than you can by looking at the surface that is shown to the public.