LA 360 - 0.030" Undersize Main Bearing Clearance Questions

I’m assuming that you are using a quality micrometer and it came with a standard to check its calibration. You then also checked the calibration of your dial bore gage with that micrometer?
If your measuring instruments check good. Measure the inside diameter of each main bore with the bearings installed and reference those numbers to each journal on the crankshaft that you checked. Then you’ll know what actual clearance is of your bearings.