Was it a slow wear thing or did it just feel loose all of a sudden? I read something a while back about how those older knobs can work themselves loose over hundreds of rolls just from the repeated winding motion. The tiny screws or the spring inside the mechanism get worn down bit by bit. That's probably why a quick check before loading is such a good habit, catches the slow drift before it steals a whole roll. Sucks to lose a day like that but your wiggle test idea is smart.