[Leon]

To add a bit to what Frank said, Burdick classified many things in his ACC, which classifies most of our insert cards, by who and how, the cards were issued. So if they were put out, or inserted, with a package of Standard Biscuits then they got a D, for Bakery, designation. If they got put out by a periodical, as The Sporting News, then they got an M designation. Burdick made many mistakes but that is mostly how he tried to classify them. That is why you see the classifying as you do.

As far as values, HOF'ers, Black Sox members, minor stars and short printed cards usually bring more money. Many of the different backs are considered rare and will also add quite a bit of value to the cards.