I don't think Knorr or Franz were con men
Why not ?
For example Franz reiterated the 6000 years of mankind's existence twice approximately 30 years apart , which was first actually used by C. Russell in the early 1900's.
Knorr was just a executive director of a expanding world wide publishing organization called the Watchtower Corporation.
Franz was the creator of the false doctrines and Knorr was just the business propagator of distributing those false doctrines to the public through literature publishing.
They were both inherently and personally involved in their acts of charlatanism.