With the passing of Jim Czyl and the Rigas, who are the authorities on this material in the U.S.? All suggestions appreciated.
I have seen reference to this new catalog for philatelic event cinderellas. Seems like James Drummond might have a claim to being the expert on U.S. cinderellas. This looks like a great resource, although, a little pricey and only half completed at this point.
Philatelic Exhibition Labels, Part one: U.S.: A to L by James N. Drummond. A catalog and check list of labels issued by stamp exhibition and shows over the years. Thousands of items are listed. Illustrated in color. 2019. Looseleaf. 894 pages.