I have seen so many times that skate tech has marked certain radius to the skate, but real ROH is 2-3mm different.
3 mm is about the difference between 3/8 inch and 1/2 inch. That's really, really bad.
It's one more reason skaters shouldn't keep switching skate shops. Not only do they have to adapt a lot, but they will sharpen away their figure skating blades in just a few sharpenings.
Does the Wissota machine make it easy to set the zero point correctly?
Your calibration shaft sounds like a good idea! There must be many professional skate techs who don't understand this issue, and don't try to adjust for quill length.
This may sound extreme, but maybe skating organizations should certify skate techs' knowledge and skill, and publish the results.
Of course individual skaters can buy a set of radius gauges, and while they are at it, level checkers, to check how their techs are doing. It's not all that expensive. But that is a lot of knowledge to expect of them.