The Watchtower always believed in an earthly class. However, originally they taught that there were 144,000 rulers in heaven, and then also a great crowd in heaven, who were the not so good JWs.
Watchtower 1927 15 January pp.19-20 "The Great Multitude," "… all the facts and the scriptures bearing upon the matter under consideration show that those who form the great multitude constitute a spirit class, born on the spirit plane."
Only people dieing after Jesus could go to heaven, so anyone not belonging to the great crowd or 144,000 were to be resurrected onto earth.