That presumes a carb was set to a given state of tuning to begin with. If during the carb assembly process the needles were simply inserted into their mounting positions only enough to keep them in place, what would you have for a state of tune once the carb was mounted?

There is no rule or requirement for a manufacturer to run an engine, only one to assemble the engine and stuff it into a box. There's no rule to test run a carb either. What engine will that carb be mounted on?