Just a couple thoughts; first I have been using Lee Safety Scales since the early '70 (along with 3 others) and have never had one "lose zero". If the OP means the sliding poise has moved, the poise is equipped with a lock and it's just a push of a small button and the setting won't move. Just checked mine the brass adjusting nut is hidden between the beams and can't easily be bumped and normal use of the scale won't move the nut. Perhaps handling the beam when setting up a finger can get down far enough to move the screw?

I was told a very long time ago "the only way to eat an elephant is one bite at a time". So when faced with a huge problem//task, I break it down into easy to handle steps. If I needed to pull 1,000 rounds I would only pull as many as I felt comfortable doing at one setting, whether it be 100 or 10. And before you know it you will have pulled 1,000 rounds, no sweat...