Here is a special find. One of those exceedingly rare all cellulose acetate dial number plates without metal backing.
This one came on a #2AB dial of a 51-C desk stand that was installed for tip-party message rate service with a 554-C subset.
By all indications this desk stand was last refurbished in 1933, as indicated by several matching dates on the unit.
The dial plate is dated II-33 on the back, and has the inscription that indicates the patent application was still pending. Indeed the patent was not granted until later in the year.
The dial plate is for a #4 dial, as is indicated by the notch for the finger stop on the edge. However, the dial is indeed a 2AB. I have found no references that indicate that these were ever found notchless for #2 dials.
By the dial card, the instrument was installed in Brooklyn, on the BUckminster exchange.