On a frame machine I have the ability to take comparative measurements side to side, upper and lower ball joint locations, measure steering knuckles side to side etc to check for bent components, on an alignment rack you see the same problems in the SAI, Included angle, set back numbers. It's why it's so important for that info to be there. You're talking about stuff that can be a few millimeters off but cause big issues. A knuckle that's bent 1/8-1/4 inch can translate into the tire being tilted in a half inch at the top of it's circumference. Same deal with the top of the frame rail rolled in the same amount. A little bit equals alot at the tire.
The alignment guy should have been able to tell you definitively if the LCA bushings or lower BJ are wiped out and actually need replacement.
Sometimes you can measure things out simply with a tape, the center point of the axle to a bake caliper mounting bolt, the distance between flats on the the BJ mounting flanges top to bottom, The lower bj location in relation to a corresponding frame hole that's the same on both sides of the vehicle, what you're looking for is a difference in numbers as compared to the side that appears good.
Probably have to get some more experienced people involved. In collision work you never assume anything is "good" until it's measured. If you don't check by measuring you end up on an alignment rack multiple times.