Pete, you might be overthinking this.

All of the postcards below are from the Pomona Public Library collection.

All of them have numbers on them...some are handwritten, some are next to the Frasher emblem...printed on the card. My guess is that was Burton Frasher's numbering system; an order number for his customers,maybe?

It would make sense for libraries to use that number as part of the description for the card.