[barrysloate]

There are several characteristics which constitute what we all agree is a baseball card:

1) It's a rectangular piece of cardboard that depicts a baseball player or several players.
2) It's typically distributed to advertise a product, such as tobacco, candy, or gum.
3) It's widely distributed to the greatest number of people possible.
4) If you collect the whole bunch of them you will be able to complete a set.

The Atlantics CdV certainly depicts baseball players, but it contains no advertising, was selectively distributed, and is not part of a set. So it does not have all of the traits we typically associate with a baseball card.

When I first started specializing in 19th century baseball memorabilia in the late 1980's, there wasn't a single collector who called a CdV a baseball card. But that definition has changed over time, and now most collectors consider it to be one.

What do I think was most responsible for that change? The slab. When the TPG started slabbing them, we started calling them baseball cards. It's just part of how the hobby has evolved.