I hope this image loads correctly.AFAIK, for most 55+ degree threadforms there is no gouging unless the cutter diameter is too close to the thread diameter. TBH I haven't modelled it out for anything other than ACME and TR...
I modeled a 1/4-20 UNC 3B hole with a threadmill with comically small shank. Then I did a boolean subtract of the threadmill from the part. That leaves a really small scallop. The maximum depth is .0001 inches (a tenth). So effectively zero, but like that flat spot where a ball bearing contacts the race, maybe somewhere it matters.
So I guess I answered my own question, but I was just too curious. Thanks gregor! I'm sure you saved myself a bunch of people from some real headache in the future.
Next question: Is it possible to use spindle orientation coordinated with a helical toolpath to cut the thread with a boring bar?