This is a Significant Operational milestone.
The flight test program lasted 26 years in total, starting in 1977. Ship 2 (N703NA) was ferried to the Udvar Hazy Center of the National Air and Space Museum from 10-16 Sep 2003, where it is now on permanent display.
To see a video of the XV-15 in flight please follow this link (video courtesy of NASA.gov).
Source: "The History of the XV-15 Tilt Rotor Research Aircraft : From Concept to Flight", M. Maisel, et al, Monographs in Aerospace History #17, NASA SP-2000-4517, Page 153