Any chance you can get a photo of that serial number? It would be very rare for there to be an inverted number. There should be 5 digits, all in line with each other.
According to Bob Kerr, a former Simplex employee told him the number was stamped on the plate before it was welded to the frame (he related a story of dropping a box of them one time & they just scooped them up, not paying attention to the order of numbers).
With a 9 as the 2nd digit, a zero should be the 2nd digit....unless it's an extremely rare model that would have a "1" as the first digit.
Is the plate missing from the other bike?
Mike Sal