In the opening scene when Maverick and Samantha are playing draw poker, Maverick has 3 queens with the Ace of Diamonds and the KING of CLUBS. When Samantha shows her hand, she has has 3 kings, one of which is also the KING of CLUBS. Maverick could have called a misdeal if he had picked up that there were 2 Kings of Clubs in the deck.
The interstitial card states that the rule they are quoting comes from an 1876 book but episodes before and after establish the year as 1872, four years prior.
The story gets the 1876 Hoyle partly right and partly wrong. Hoyle does *not* say that straight hands must be decided before a game begins; in fact, it doesn't even mention them, making them unplayable simply by not recognizing them. Experienced players of the day would have known this, and would have made sure before play began whether or not they were acceptable a table rule. Thus, Samantha's ruse not only wouldn't have worked, it would have never come up.