I’m curious about this too. While most of my 39 series mags have the black “plastic” follower and work smoothly and without problems, I recently acquired one with the stamped steel (“figure 8”) follower and in what little time I’ve had to shoot it, it has done great. Are you perhaps talking about the very early flat followers used In the very first Pre-Model 39 mags, ACEd? I’ve never even seen one of those and have no experience with how they function.

IIRC, my Model 52 mags have the stamped steel followers and they manage to feed 38 Specials reliably.

Inquiring minds want to know.
Froggie