That is an interesting fact. Guess it begs the question as to why the Army declined to release the data. That being said, Phrobis/BUCK undoubtedly did their own stress tests to ensure the bayonets did meet Army specs. We know from reports the tip of the bayonet as found on the prototypes was weak, and this problem was subsequently redressed in the production bayonets. I have read there were concerns about the fuller possibly making the blade weak, and the tang/rod may have also been an issue. The latter seems evident from the Phrobis product improved prototype held by one of our Forum members:
http://www.quarterbore.net/forums/showthread.php?t=2900. I recall seeing another Phrobis P. I. M9 with what looked like a nylon hex rod in the grip as well. In addition, the insistence of the USMC wanting a solid-tang incorporated in the 1993 trials bayonets submitted by BUCK also shows concern over the threaded tang/rod.