There are so many things here that don't sound right BUT, when sighting in a rifle there are so many variables that it could happen. Did he take into account Coriolis drift, wind drift, wind suppression or lift, gravity anomaly(I'm always 5 lbs lighter at my daughters house), a shift in the space and time compendium, even magnetic anomalies( being in MI he is close to large iron ore deposits(I hunted northern WI and MN and have been in areas that you compass would just spin around) the list just goes on and on.
One thing for sure just don't shoot at anything farther than 100 yards, take another rifle for the long stuff. Hunters do that all the time they carry a shotgun for short range and a rifle for long range.
A four foot square of paper moved back at 10 yard interfolds from 100 yards to 200 yard would surely determine the problem or at least let him know the maximum range of his rifle.
I'd spend days at the range just to figure out what the problem is, work, family that is just fluff compared to figuring out rifle stuff.