Complex sentence: Unlike the other two, General Drafting did not sell its maps to a variety of smaller customers, but was the exclusive publisher of maps for Standard Oil of New Jersey, later Esso and Exxon.
Split into simpler sentences: Unlike the other two, General Drafting did not sell its maps to a variety of smaller customers. It however was the exclusive publisher of maps for Standard Oil of New Jersey, later Esso and Exxon.