If you shut off the air pressure going to the valve, you can manually turn the classic velocity adjuster using just your fingers. That made it easy to cheat in the field during tournaments.
The old velocity locking rings screwed over the threads on the velocity adjuster and tightened against the back of the valve effectively locking the adjuster tightly in place. Some locking adjusters were complete replacements for the stock adjuster and had larger thumb wheels instead of allen key holes. Those adjusters used locking allen screws to prevent field adjustment without tools. Others had replacement adjusters that had a smaller diameter so that a protective cap would cover the adjuster to prevent field adjustment.
The retro valves were designed with an oring providing tension on the adjuster, so that you always needed tools to adjust the velocity.
Most fields aren't knowledgeable about mags, so I doubt many refs even know that a classic mag can be velocity adjusted in the field without tools. To be legal though, you do need to have a velocity lock on the adjuster of a classic mag.
Except for the Automag in front, its usually the man behind the equipment that counts.