Is there one company which would have been more likely to have 18 marbles in their bag than another?
My guess before today would have been Peltier, possibly as jobbered by Rosenthal. And as of today, my Rosenthal guess is a little firmer. In December of 1931 Rosenthal advertised "Sure-Shot Glass Marbles" as "Special Numbers for Jobbers". The bag pictured is the double compartment one Berry Pink patented, which has more than 18 marbles.
But is that wishful thinking? Did multiple companies sell 18 marbles per bag?