I believe there was an original Marvel comic at the time that depicted Han losing his reward from the Alliance.
http://starwars.wikia.com/wiki/Star_Wars_7:_New_Planets,_New_Perils!
His reward was stolen by pirates allowing Marvel to maintain Solo exactly as he was in ANH until Lucas would specify otherwise.
In one issue Han actually solves his debt problem with Jabba (or rather the early walrus-mam version), only to have Marvel quickly create an excuse for Jabba to change his mind back in the last issue before ESB once they realised that Han was still in debt in the movie.