that were developed over 100 years, with the rulebook written in blood (literally).

Fly, take measurements, make corrections, repeat.
Expand the envelop in management pieces. Repeat.

Looking back on it, they really didn't make all that many intermediate flights, at least the powered ones. They made the first powered flight last Dec 17th, breaking Mach 1. They broke the landing gear on that one. If memory serves, they made only a couple more powered flights before going for the X Prize. That's pretty aggressive.

They had problems and had to make some modifications. Standard flight test stuff. Rutan started his career as a flight test engineer for the Air Force. He has about 40 years of experience in the field and isn't about to violate the rules.