I think your'e both saying the same thing but you're looking at it two different ways. The SAMMI spec for the gauges is bigger than the SAMMI spec for the cartridges. Its comparing apples to oranges.
The Go gauge is ground at the minimum SAMMI tolerance for the chamber, which should be only slightly above the SAMMI tolerance for the cartridge.
Do the two standards overlap? I confess I do not know, but I do know that if you want any factory ammo to dunk right in without a hitch, then you had better go about .002 deeper than the Go guage.
The beauty of the Savage barrel setup, is that after you bottom the barrel out on the gauge, when you torque down the locknut, it gives you that little extra gap on the gauge. The nut just pulls the barrel a couple thousandths away from the gauge, and voila! perfect headspace!
The only worry is that if for some reason (yeah I know, chance in a million) the threads gall, or have trash in them, or anything other than the headspace gauge stops the barrel from rotating, and you torque down the lock nut, you could actually have excess headspace. That is why it is a really good idea to either drop in the Not-GO gauge, or put two layers of scotch tape over the base of the Go gauge to make for darn sure you are in spec. If you are renting the gauges, then you get both and it costs you nothing to check with the Not Go gauge. If you ponied up the $$$ for your own headspace gauge, and saved money by only getting the Go gauge, (I have done this, I hang my head in shame) you can get by with the tape trick.
All I'm saying is that you need to check just to be sure, because on a Savage, you could have .002 over GO or .050 over go and it would feel exactly the same. So do yourself a favor and check.