BW001 - "To the Isshu Region! Zekrom's Shadow!!" BW122 - "Reshiram VS N! Beyond Truth and Ideals!!" BW142 - "My Dream, Pokémon Master!!" - If I'm not wrong, BW001 and BW122 were the only times Zekrom and Reshiram were mentioned in a title: the episode Satoshi came to Isshu alone with Pikachu, and the episode ending his adventures in the region together with Iris, Dent and N (next episode, he departed for Kanto through the Decolora archipelago). - Zekrom is listed for BW142 so if he's not a flashback or a figment of imagination... yes, they want to give us a feeling of closure: first and last episodes of Best Wishes! would be Zekrom's only physical apparitions in the anime (not counting flashbacks, dreams or papAraragi telling the legend). Plus, BW123 - "Farewell, Isshu! Setting Sail Once Again!!", which begins the Decolora arc, had Satoshi dreaming about Zekrom and Reshiram; only to apparently see Zekrom at the end. So, yes. Small meta book ends everywhere.