Okay, a more careful reading of my Charlton reveals to me that the "new inserts" started making their appearances a bit before before GPZ and FDZ. It seems that the earliest "new inserts" reported were GOT, BDP, AWI, EVZ, FHZ, and BJR.
Did these prefixes really start appearing as far back as 1996? It doesn't seem like that long ago. But then I've never really paid much attention to insert notes before, so please forgive me if I'm asking dumb questions.