A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 10 September 2014
What happens if i put another players card in my hand using Press the Advantage (during the sequence) and later on use an Overwhelming Chaos? Is the other player's card shuffled in my deck? What if I'm on a tournament and my sleeves are different? Do i have to take off all my sleeves or i can play with a marked card in my deck (as an exception)?
Relevant text:
Overwhelming Chaos Open: Each player shuffles his hand into his deck, then draws as many cards as he shuffled into his deck.
Press the Advantage Battle: Target a non-Ring card in another player's discard pile. If the card was discarded by a Strike First this turn, put it in your hand, and you may target your Scout and discard a card to search your deck for a Show No Mercy, show it, and put it in your hand; otherwise, remove the first target from the game. You may take an additional action to play Show No Mercy.
Jon Palmer (rules official), 10 September 2014
What happens if i put another players card in my hand using Press the Advantage (during the sequence) and later on use an Overwhelming Chaos? Is the other player's card shuffled in my deck? What if I'm on a tournament and my sleeves are different? Do i have to take off all my sleeves or i can play with a marked card in my deck (as an exception)?
Relevant text:
Overwhelming Chaos Open: Each player shuffles his hand into his deck, then draws as many cards as he shuffled into his deck.
Press the Advantage Battle: Target a non-Ring card in another player's discard pile. If the card was discarded by a Strike First this turn, put it in your hand, and you may target your Scout and discard a card to search your deck for a Show No Mercy, show it, and put it in your hand; otherwise, remove the first target from the game. You may take an additional action to play Show No Mercy.
From the CR:
If a card a player owns is about to enter another player’s deck, it enters the owner’s deck instead in the same manner.
Since you didn't shuffle the card into your deck, you won't get to draw from it for Overwhelming Chaos.