According to the IPG, when the opponent of a player who missed a trigger chooses to put it onto the stack, “No player may make choices for the triggered ability involving objects that would not have been legal choices when the ability should have triggered. For example, if the ability instructs a player to sacrifice a creature, that player can’t sacrifice a creature that wasn’t on the battlefield when the ability should have triggered.”

I have been told that players are allowed to make such choices if it cannot be publicly verified whether such objects would have been legal choices when the ability should have triggered. For example, suppose Player A misses Acquisitions Expert‘s triggered ability, then Player B draws for turn, then the missed trigger is acknowledged and Player B decides to put it onto the stack. During resolution (assume Player A’s party is now 1), Player B may reveal the newly drawn card, if and only if there has been no point after the ability should have triggered during which Player B had no cards in hand (so that whether a particular card was in the hand when the ability should have triggered cannot be deduced). Is this correct?

If so, does the game use the concept of sets from the IPG in making this determination? For example, suppose Player B for whatever reason wants Acquisitions Expert’s triggered ability to go on the stack, but does not actually want to discard. Can Player B keep the card drawn for turn in a separate set away from the rest of the hand, then play out the rest of the hand, then acknowledge and put onto the stack Acquisitions Expert’s triggered ability while only the drawn card remains in hand, and not reveal/discard that card because it can publicly verified as an ineligible choice in virtue of having been kept in a separate set?