I don't know how many White's were produced, I only recall ever seeing 1 factory White (besides the Crane Bros custom 38's) - I believe it was a plunger style. So, the small number compared the the 7500 +/- Knight 45 1:20's might be why.
After talking to a few of the Knight Team shooters, it seemed the manufactures match was shot from different positions (including tree stand) and distances only to 200. With that, it seems many (not all) were RB -bench shooters and did not shoot a heavy bullet (300gr max) or charge. I have no idea what the other Teams were shooting (load). Today's NMLRA guys shooting Knight's w/ 20 & 18 twist are most all using heavier bullets (like Whitworth 500+) and achieving very good results. Even a former Knight Team member who shot a 295gr bullet at May's inline match realized he needs a heavier bullet to compete at the animals.
Jim S. shot really well in spring of 2014 with his Ultimate, the Marsh Bros shot their Ultimates in the IN-line AGG this past June. They again like Jim have struggled for some reason since last year.
So, really only Knight and Ultimate are the only 2 mfg that have shown up for the match. In Ultimate case 4 guys did show up last fall and I have to give Knight credit as they have been supporting/shooting at every match. If you consider Ultimate a custom, then really only Knight is the only mfg.
I think other brands can certainly compete at Friendship, but I don't think the avg MML will put in the time to experiment with his rifle.