How do you know when an encrypted book is solved?

[doranchak]

If there are a multitude of possible solutions, then it's not reproducible.

Among the many wrong codebreaking claims I've encountered, there are some whose steps are comprehensible and some that aren't.

In the former case, at least we can repeat the steps that lead to the proposed solutions and then demonstrate why they lead to other plausible ones.

In the latter case, they are "not even wrong", as Wolfgang Pauli liked to say.