> someone on your own production line can introduce a new step to your truck manufacturing process that no one noticed?
That's actually not unusual at all.
It's perfectly common for an engineer to order that a hole be made in a given location on a given part without specifying that coolant should be used, or the spindle speed of the drill, or how the part should be held in the machine, or that the hole should be deburred.
Manufacturing is skilled work.