As a gunsmith, I've sighted in at least a thousand rifles for others over the years and have never had anyone come back and say it was wrong for them.
At a turkey shoot, four of us used the same rifle to fire one round each and all of us hit the 1" target center on separate shooting rounds, winning 6 turkeys that day. We were shooting prone over a log at 100 yards and the rifle was a .22-250, Rem 700 ADL, 2-8X scope, shooting 55 gr, Sierra Semi-point handloads.
At another shoot, on a bet, my wife shot a perfect pinwheel with the same rifle; her one and only shot in competition, 7 months pregnant, laying on an angle, due to her belly. It wasn't a pretty scene, when other wives were asking her to teach their husbands how to shoot. Most of the guys never returned the next week, so they never held turkey shoots again.
Well, if folks do that with apparent succes, I doubt they're able to shoot no worse than about 1 MOA with the sights used. Especially when 1 or 2 shots have less than a 10% chance of represent where the zero's at. If you're both shooting about 2 MOA or thereabouts, it is quite possible that the same sight settings will seem to work.
With a rifle and ammo capable of 1/4 MOA accuracy and both shooters able to call shots within 1/3 MOA of exact, then you'll see the difference in sight settings.
Picher, I think your own and your customers/relatives accuracy standards and levels ain't enough to discriminate the small zero differences that exist between people and a given rifle and ammo. No slam intended, but we all don't have the same levels of marksmanship.
PS: Most of the top prone competitors shoot with their bodies on an angle; that's been happening for over a century.