There's a famous photo of Chu Berry holding a Conn tenor that's really in between the typical 10M and the typical NWII. You can clearly see the curved high E key and the bell keys on opposite sides of the bell.
What instruments he might have played before and after that photo was taken, is anyone's guess.
The main mechanical differences I'm aware of between 10M and NWII are the modified LH table (six of one, half dozen of the other to me), the bell keys all on the same side (no real effect to the player), and the bis Bb being relocated (10M is better IMO). Also the octave mechanism is changed - the 10M is much more complex but also easier to regulate and have it stay.
There seems to have been a lot of variation in build specs and engraving right around the time of the model transition. Keep in mind that at the time no one knew or cared about these fine distinctions, and Conn just called it "the Conn tenor saxophone". You went to the music store and they had some tenors - a King, a Martin, a Buescher, a Conn, a Selmer. You didn't compare photographs or ask for input from strangers on the internet. Whatever the music store clerk told you, plus the minimal information in the manfacturers' catalogs, plus the input from your friends/colleagues/teacher, was what you knew about the instrument you purchased.