Hi, the numbers reflect the designer - RSW being Ronald Stennett Willson, of course. When RSW left Wedgwood for Langham, many of his designs were relabled SG, with some slight variations brought in. Interestingly, when RSW started Kings Lynn Glass in the lates 60s he couldn't find English glassblowers capable of the thin stems on the Sandringhams and Brancasters and employed Austrian glassblowers to make them.