It is roughly an unspoken rule:
Pencil and Paper -> nothing past or including Enigma
The way I see it is that the previous plaintexts were made for a purpose, Sanborn is communicating some kind of higher message to people. His purpose for the first three plaintexts is not just to give away Enigma settings, he is the master of sculpture…if he wanted to he could hide them a better way.
Also, Enigma is quite messy when you jump into the question of "Which Enigma machine are you using?" since throughout the war there were many different types of machine, each with different numbers of rotors/reflectors available, different numbers of rotors to be put into the machine and even different wirings of of the rotors too.
The challenges on this site were contrived in the fact that we were told which machine to use and quite a lot of extra information.
Theoretically, if we ignore the actual machines that were made, the Enigma has a massive keyspace…because then the rotors can each have any permutation of the alphabet wired up.