Just to follow up on laumac's comment, the booking instructions tend to be a large part of the secret sauce. In this case, we fully verified them and all the flights were bookable at the time of verification. We disallowed a few itineraries that didn't properly visit all continents. As an aside, it was interesting to define what countries fit in which continents. For example, Guam, Curacao, Turkey.

Yes, the experts give step-by-step instructions on how and where to book.