Irving Kaufman “may have been the most recorded singer between 1914 to 1930.” He was also my great-grandfather (father of my dad’s mother).
He recorded under a variety of pseudonyms, as the lead singer and backup vocals, working regularly on local and coast-to-coast radio. “He was paid a flat fee each time he recorded, never royalties.” Here’s a link to a lengthy Irving Kaufman bio.
My dad sent me a link to the Library of Congress jukebox, which has a number of Irving Kaufman recordings (and probably a number of his pseudonymous recordings too). Here’s a tune from April 7, 1914, entitled “California and you”: