I've had situations where this could have been relevant come up every now and then.

For example, if AP casts Brainstorm and puts the only Island in his deck on top of his library and then uses a Polluted Delta to put one of them into play, is NAP entitled to know that the Island put into play was one of the top two cards of his library?

Conversely, would AP be entitled to obscure the position in the library the card was found at by having the opponent look away while retrieving the card? Or is it a case where NAP has to have sharp eyes to see that the card came off the top?

Thanks rules experts!

Nothing in the rules entitles opponents to know where a card was located when it was searched for (and presumably found) in a hidden zone. Many “tutor” effects require you to reveal any card that's found, to verify that it meets the characteristics specified (e.g., “Search your library for a creature card with converted mana cost …”).

If the player resolving the “tutor” effect thinks it's to their advantage, they can take reasonable steps to hide the previous location of the card (but let's not go off the rails, here).

d:^D

Edit: unless, of course, you're restricted to searching the top 4 (think Aven Mindcensor) - even then, which of those top 4 isn't public.