I'm not too sure what you're saying here "The 'framers' could POSSIBLY set one wall overhang at 16".
Overhang is determined by the "tail" of the truss. Trusses are set with the "point" (intersection of the horizontal seat and the slope of the tail) flush with the outside edge of the top plate.
What probably happened was the back wall was pushed out when they were sliding the trusses up and then toenailed down with the seat where it should be. Meanwhile the guy on the front end of the house lines up the seat with the top plate duplicating the shape of the back wall. Or after the trusses are up and not properly braced they were pushed back by something.
The least likely scenario is the walls got bowed AFTER the plywood was installed. I'd be inclined to use impossible here rather than "least likely"
We once racked a prefabbed place 3/4 inch. Place came with siding and windows all installed. When we put up the trusses we didn't realize we moved the wall 3/4 inch out of plumb and when we did the attachment at the opposite wall the seat goes where it belongs duplicating the configuration of the other wall.
Your comment about setting the overhang at 16 inches and then duplicating on the other wall is wrong.