Greg Filardo writes, "On the Aeolian pin-end [65-note] rolls, a number
appears on the back side of the leader."

I was told many years ago by Vern Netzow that the number on the back
of the leader refers to the number of rolls issued of that particular
title and that the matrix remained consecutive for their "stencil rolls"
(rolls sold under other brand names by music stores, department stores,
etc.)

United States Music rolls used a similar system encoded to the _very_
early roll labels and later would issue sometimes two rolls of the same
tune and this would be indicated by a letter after the later's serial
number.  Whether Mr. Netzow's information is correct, I do not know.

Karl Schröder