This number force was described by ACP Medrington in the oddly titled, A Dozen of Magic for Practical Conjurors, 1917, p. 31. While the stack was related to the principle that would later be called the “14/15 Force”, Medrington's stack guaranteed a force of the number fourteen every time. This was due to the use of short cards to guide the cut.
The idea became more widely used in the 1920s. Stewart James notes that the stack was in use within an H. S. Paine release from 1922; see Stewart James: The First Fifty Years, 1989, p. 151. Walter B. Gibson also used such a stack in “A Marvelous Prediction,” published in his book Popular Card Tricks, 1928, p. 38. Theodore Annemann does the same in the context of the trick “The Premier Book Test,” published in Annemann's Mental Mysteries, 1929, p. 1, and later in Encyclopedia of Card Tricks, 1936, p. 221.
Karl Fulves, in Prolix, No. 5, 2009, p. 287, points out that Charles Jordan was an early pioneer of the general principle, with tricks such as “Psychic Prediction” and “Fate and the Joker” from Four Full Hands of Down to the Minute Magical Effects, 1922, p. 34 and 35 from the 1947 edition, respectively. Fulves also points out T. Page Wright's “A Prophetic Card Discovery” in The Sphinx, Vol. 23 No. 3, May 1924, p. 88, which relies on a 14/15 stack. Wright in turn cites an unspecified trick of William Larsen, which Fulves surmises may be “Prophesied Discovery” in Glenn Gravatt's Second Encyclopedia of Card Tricks, 1936, p. 76. This is a good guess on Fulves's part because Wright and Larsen actually teamed up to release The L.W. Card Mysteries, n.d. (c. 1928), p. 3 of the second edition, where they taught that very trick, “A Prophesied Discovery”. Larsen's trick, however, doesn't use the 14/15 stack. Instead, it uses a different stack to achieve a similar end result. Instead of cutting, the stack allows piles to be dealt with different numbers of cards in each. No matter which pile the spectator picks up, all the values add up to ten.
Wright had a competitor in 1924. H. S. Paine, that year, advertised “A Remarkable Prophecy” in Catalog No. 11 of his Chicago Magic Co. “A Remarkable Prophecy” is identical to Wright's “Prophetic Card Discovery”. In Stewart James in Print: The First Fifty Years, 1989, p. 151, James, a reliable historian, wrote that Paine had released this trick “as early as 1922”. However, Steve Beam and George Daily checked all the Chicago Magic Company's catalogs from 1921 through 1927, and found “Prophetic Card Discovery” offered only in catalogs No. 11 (1924) and No. 13 (1927); see Beam's Smokers, 2022, p. 27. Beam's book offers a detailed history of the 14/15 Principle.