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Key Card
This principle is explained by Girolamo Cardano in his De subtilitate (1550, early in Book XV), and has been a staple of card magic ever since. See John M. Forrester's English translation of De subtilitate, Vol. 2, p. 754. Forrester mistranslates playing cards as pieces of paper, but the rest of his translation for this entry is clear enough.
Key Card with a Spectator Shuffle
The understanding that a key card was very likely to remain next to the selection if a spectator is allowed to give the deck a shuffle is mentioned in Thomas Johnson's Dainty Conceits, 1630, ninth unpaginated page. Johnson's description reads: “Marke you the bottom Card privily, and then opening the Cards, bid one take what Card him liketh, and when he hath drawne the Card and seene it, lay that Card close to your knowne Card, and then give him the Cards to cut or shuffle, whether he will, and [s]ay that you can tell him his Card, or in drawing know when it commeth out, which easily you may doe, for that it will come either the next before or the next after the marked Card.”