Having solved the first problem (finding the number of legal routes), I've been pondering on the second problem: How to prove that a wrong answer is actually wrong. My preferred choice is to prove, by math, what is correct, but that obviously only works if the target audience understands and accepts the math as correct. I'm willing to give that one more try later (I've found an even easier way to explain it), but I've also been working on other options.
For the other players who have presented their calculations, the natural thing is to point out errors in their calculations. Some have made very elaborate explainations, which is a good thing, because it's easy to point out what is right and what is wrong. That's "good science". For those just presenting a number, I can think of no way to prove that number wrong, except if they present a very small number, in which case one can counter with a list of legal, non-duplicate routes longer than that number.
However, as I understand it, Dungeness is actually compiling a list. Checking if a list is right or wrong IS possible. I've made one program that checks a list for "illegal" routes (fast), and one that checks a list for duplicates (slow). Using this, I've also compiled a list of all legal, non-duplicate trading routes myself. This means that if Dungeness' list is presented in some way (I need to be able to import it, preferably to Excel or MatLab), I DO have a way of proving if that is wrong: If it contains illegal routes or duplicates, I can point out those routes. If it is incomplete, I can check which routes are missing, and present a legal route that is NOT in the list. So, now I'm just waiting for Dungeness' list to be presented in som downloadable format