In a local group we are discussing about this situation.

In AP upkeep, he has Aether Vial with 5 counters, and Sylvan Library in a 7-cards hand; he plays Brainstorm and draws Goblin Dark-Dwellers and other two cards, keep goblin and sylvan in hand, still in upkeep, AP uses Aether vial to put Goblin Dark-Dwellers into the battlefield and targeting Show and tell.
Show and tell resolves and AP puts Sylvan Library, then goes to the draw step and wants to draw two additional cards.

1- AP ask you how can complete legally by drawing three cards and return one or two
2- You receive the call when AP has resolved Sylvan ability, AP distinguished only the three cards from sylvan

I'm not sure about how to act in first case, should be better tell to AP if he uses Sylvan this time will fall into HCE

In second case… it's fine to reveal AP's hand and the two top cards by apply HCE fix?, in my opinion there are up to 6 unknown cards during this turn, two at top and up to four ones in AP hand.

Regards

Edit: AP always can return cards from sylvan draws to not commit any infraction

Edited Jose Miguel Sanchez Navarro (Feb. 19, 2016 04:43:39 AM)

Wow, that was a lot of work - and way too many corners for my taste! - to get Sylvan Library into play during upkeep and thus confusing things with the Brainstorm. When you have to work that hard to construct a scenario, then it's probably best to just discuss it with your friends, and not make all of us “suffer” - LOL!

The solution is a whole lot simpler: people who play with Sylvan Library are responsible for proving which cards were drawn this turn, and thus can be put back for the Library. If they fail in that, we simply ask them “how much life would you like to pay?” If the answer is anything other than “8”, and they can't prove which cards were drawn this turn, then we have a Hidden Card Error.

The opponent looks at the cards in hand - not the other two cards, on top of the library - and chooses “a number of cards equal to the number of excess or unverified cards” to be shuffled back into the random portion of the library. (Remembering to set aside the two known cards put back by Brainstorm, and any other known cards.)

Now, if AP draws three during their draw step and keeps them separate from their hand, they can easily put back two of those three, and we won't have any problems, at all.

d:^D