A G68.2 / Probing Question...

I am working on a Doosan DVF5000, trunnion style 5 axis machine. In MasterCAM, I've programmed with X0, Y0 as the center of the part and Z0 as the bottom locating face of the part. The intention was for the part to share the same center as the machine table and not use any dynamic offsets. However, the forgings are varying and we are using the probe to establish centerline of each part and setting G54 X and Y offsets that way. The center of each part is varying up to about .050".

So,

X0 Y0 in MasterCAM = Center of Part

X0 Y0 at G54 on the machine = Center of Part, but the Part is not exactly on center of the rotary.

If I understand G68.2 correctly... I can use G68.2 X0 Y0 Z0 I__ J__K__ and the machine will calculate the difference between where G54 X0 Y0 are and the center of rotary axes as the program moves through the different rotations? How can I verify that this is working accurately?

I have a feature that I am putting in at B30.482 C0 using G68.2. It is just a hole at X2.815 Y0 at that angle. When I put the hole in, I go back to that same location using G68.2 again and probe the hole and it tells me the hole location is X2.845 Y0.0003. I can accept the Y difference, but how can I possible get a .030" difference in the X after I just put the hole in? What am I not understanding? I'm stumped...

Any insight would seriously be appreciated. Thanks guys...