Looking at the site I was just on, the explanation is they usually have been known for their small, $12 - $15 lights and they decided to give people the opportunity to collect the "B"ig-ger version, which is more detailed and more comparable to Harbour Lights at less than 1/2 the price; so 231S would be one of the small, less detailed, plain-ol'-ugly ones and the 231B would be the greater detailed Big'un!
laugh

Steve

Health through education, for a much misguided nation!!