Ruling Reprinted Cards Before Prereleases

[Elbow]

I know you are able to do this after prereleases, but are you able to use copies of a card that has not been released even if that card is legal in standard play?
For example, lets say Pikachu was printed in XY. The same exact Pikachu (with different artwork/same text) was reprinted in a later set while Pikachu XY is still in format. This set has not come out, but people have managed to get access to packs/singles due to stores breaking dates. Because Pikachu is already a legal card, can I use this new Pikachu? Does this apply to trainer cards as well? Do mind that this question is before the official prerelease date. Thanks.
~Elbow

 

[My Little Keldeo]

From the official tournament rules on Pokemon's website:

1.5. Unreleased Cards
From time to time, players will acquire cards from a new set prior to its regular release date, usually via a Prerelease. These cards may not be used in sanctioned tournaments until the regular release date of the set, as outlined in Section 13.1, with one exception. Cards that are already tournament legal which have been reprinted in an unreleased set may be used as long they are easily identifiable as a reprinted card. This is typically only an issue when a reprinted card receives new art, though other factors may create a similar issue. These cards should always be played with the most recent wording of the tournament-legal version of the card

Yes, you are able to use reprinted cards from a set that is not yet legal, provided that the cards are already legal for play in the tournament's format. It doesn't matter if the cards came from a prerelease or someplace else. Any issue involving this can easily be resolved, as most players and any staff should be able to tell what's a reprint and what isn't from the text alone (in the case of a Pokemon like the Pikachu you mentioned) or the name in the case of a Trainer Card or Energy, which is the more likely case.