It's worth noting 2K International covers the publisher's activity outside of the US, so even if the tweet is accurate, it might not reflect the release date in the States. As PlayStation Lifestyle reported in December, it's a date that's popped up before, that time on a NewEgg listing - that said, NewEgg lists the game currently for April 15. We've reached out to 2K Games for comment.
Looking back, it feels like the Vita port was as much in the limelight as the action-RPG shooter itself, after Gearbox received countless questions about the handheld venture it seemed so keen on. Thankfully, 2K Games and Sony put an end to the seemingly endless discussion by announcing it at Sony's Gamescom conference, and unveiling Divekick studio Iron Galaxy as its developer.
Update: Via the @2KInternational account, 2K Games said the March 18 date is incorrect.
"We apologize for a tweet about a release date for Borderlands 2 on Vita which was posted in error. The release date mentioned is incorrect," reads the 2K tweet.