the two most common gage brands are Forster and Clymer. Clymer has a rep for tightly adhering to the standards. Forster gages reportedly tend to wander from spec.
sooo if one smith used one brand and the other guy used another you could get different results.
-also some gages came with cut outs to use in the m1/m14 so you didn't have disassemble the bolt. Personally I would disassemble the bolt. If the cut wasn't there and the smith didn't strip the bolt then the readings were bullshit as the ejector was pushing damn hard on the gage to get any reliable reading. Op rod and spring out, bolt stripped, insert gage into spotless chamber and gently finger close the bolt on the gage. If the right lug is up any amount above the reciever than it does not close on that gage.
-like was mentioned before the saami min and max don't match up with the military min and max. IIRC the mil min is just under the civi max. IIRC civi 1.630 - 1.634 or 5. mil was 1.633 to 1.638 ish. and the mil national match was different than either of those. Those numbers are off the top of my head and I guess they merely show the relationship of civi to mil.
I always figured ideal was 1.633 headspace, just right for civi and mil cartridges with a good safety margin.