Time to add to the confusion...

Today, in my pre-ban magazine hunting travels up in the "live free or die" state, I found a LEO/Export-marked 4006 Magazine (from 1994-2004, obviously) with a yellow follower. It didn't look tampered with (it was in a wrapped, labeled package but not the well-known S&W retail package of the period. And it had the "Accu-Glide" roll mark on it.

This would be the first evidence I've ever seen that you may not be able to assume that a yellow follower 4006 magazine is always a pre-ban.