This has been known for a while, but some people still speculated it would only be the Pokémon Center booster boxes that would contain the Reshiram promo. Every booster box distributed in the UK, USA, and Canada will be the “enhanced” version. This footage of a booster box opening shows that the enhanced version is not exclusive to the Pokémon Center.
The Reshiram illustration will also be part of the actual set! (Third image) This means you don’t need to buy an enhanced booster box if you don’t want the stamped version.
by JersenPyro