Complex sentence: Dorsey F. Wheless, and W.L.Kinkead were cataloging US National Christmas Seals for Scott's Monthly Journal in 1928, whose work was incorporated into Scott's Specialized Catalogue of US Postage Stamps 1935.
Split into simpler sentences: Dorsey F. Wheless, and W.L.Kinkead were cataloging US National Christmas Seals for Scott's Monthly Journal in 1928. Their work was first incorporated into Scott's Specialized Catalogue of US Postage Stamps 1935.