Laurence Stockton Helffrich, Collector. Poster Stamps, #1918. Division of Rare and Manuscript Collections, Cornell University Library.
Laurence Stockton Helffrich, Collector. Poster Stamps, #1918. Division of Rare and Manuscript Collections, Cornell University Library. https://archives.library.cornell.edu/repositories/2/resources/3442 Accessed September 03, 2026.
