'I don’t think I did either from scratch. In the 20th Anniversary Edition developer commentary, Schuler explains (and Blum agrees):
None of these levels were created from scratch. Blum III, Richard 'Levelord' Gray, Randy Pitchford, Keith Schuler, and George Broussard. Levels in the new episode were designed by Allen H.
The Atomic Edition adds a new fourth episode known as The Birth.