what size st louis

[Smokesman]

At our restaurant depot you can buy fresh st. louis cut w/o buying a whole case - think they are 2 per cryo - $2.99/#. They also have "light" spares for $2.09/# and "medium" spares for $1.99/#. I asked the meat counter what the difference was between light and medium and he said it is a grading - from worst to best - light, medium, st. louis, loin back (baby back). If that is the case though then why are lights slightly more expensive than mediums? Mediums seem to have more marbling than lights. This is the only place I have ever seen spares listed this way. Any insight?