The situation: Anson and Noah are sitting down down for round three of five. After shuffling and presenting, they each draw their opening hand, at which point Anson calls you over and explains that he forgot to desideboard from his previous match. After a few brief questions about the situation, you don't suspect that Anson intentionally forgot to desideboard. What is the fix? What about if this had been discovered after the game had started?

Edited Hank Wiest (Nov. 12, 2015 05:43:29 AM)

Let's have a look at our beloved JAR:

A player has illegal, insufficient, or another player’s cards in his or her deck
Remove any cards that shouldn’t be in the deck, put back any cards that should, then add basic lands of the player’s choice if the deck is below the format's minimum size limit. Any cards that are added to the deck should be shuffled directly into the library. If the error was discovered during a draw effect, have the player complete the draw effect after the deck is fixed and shuffled. Encourage players to count their deck and present their sideboard (face down) to their opponents before starting a game to avoid these errors.

Consider drawing an opening hand to be a draw effect, so fix the deck by desideboarding, replace all SB cards in Anson's original opening hand by a random card from his adjusted library, and continue. If he notices during play, the same fix works: if he draws a SB card, replace that freshly drawn card by a new card after fixing his deck.
And what if Anson only realises during the game that a card should not have been there? Well, if it's no cheating, just fix it so thay can play their game… Regular isn't that complicated ;)
Don't forget to thank Anson for calling you over!