Reinhard Müller found this method of palming a card from the center in F. W. Conradi's in Der Moderne Kartenkünstler, 1896, p. 13. Conradi claimed the sleight as original with him.

It appeared in English as part of Adrian Plate's excelsior change in August Roterberg's New Era Card Tricks, 1897, p. 22. This was a steal of the bottom card of a double, rather than one from the center of a deck, but the sleights are related.

A closer precursor to the now-traditional side steal appears in Mahatma, Vol. 5 No. 2, Aug. 1901, p. 495. This is by Hal Merton (stage name of Walter G. Peterkin) and was published eight years prior to T. Nelson Downs and John Northern Hilliard's The Art Magic, 1909, p. 143, where the first description of the side steal is usually cited. Merton used his left thumb to push over the top card of the lower packet as the right hand moved to replace the upper packet. This delivered the card into position to be palmed, identically to the standard side-steal handling. A closer handling to Downs's—using the left fingers beneath the card to be stolen, rather than the thumb above—appeared in a later issue of Mahatma. It was published without credit or byline in Vol. 8 No. 2, Aug. 1904, p. 17.

The Merton, Downs and anonymous handlings may have been harbingers, variants or merely echoes of the Side Steal as done by Nate Leipzig. Dai Vernon was unwavering in assigning the Side Steal to Leipzig (see Dai Vernon's Tribute to Nate Leipzig by Lewis Ganson, 1963, p. 25), and that attribution was tendered by others in the early 1900s.Downs may have been splitting hairs in publishing his handling without mention of Leipzig, as Downs extracted the peeked-at card from the center of the deck and took it immediately to the top, while Leipzig took the card into classic palm.

See also Deliberate Side Steal and Clip Steal.