Exposing fraudulent historical sources

Are there Chinese or Tai sources for Yunnan that can't be trusted?

This question logically arises after reading Dr. Geoff Wade's recent thorough exposure as fraud of the 1418 Ming map used to support Gavin Menzie's pop history book "1421: The Year China Discovered the World."

The really scary thing is how many people uncritically read and accept this book without looking further into the matter. I'd love to use the book and the map in a critical thinking course, but then of course I'd have to buy copies of it which is really morally unconscionable.

Dr. Wade certainly motivates us to take a closer second look at source authenticity. Unfortunately, none of the manuscripts in the Burmese or Thai national libraries are accessible to do this.

Here's another relevant link with criticisms of the book.