The novelization of Iron Man 2, however, contained a surprise. The New Element is referred to as vibranium by name, meaning Tony created it and that it didn’t exist before Iron Man 2. And for a brief period, that was canon in the MCU. Iron Man 2 opened in 2010, and it took over a year for the explanation to be retconned. Captain America: The First Avenger -- released in 2011 -- formally redefined vibranium as “the rarest metal on Earth,” and stipulated that supplies of it couldn't be readily duplicated. The small amount Howard Stark had gathered was just enough to create Cap’s shield.
BUT this was swiftly retconned/hand waved away
Recognizing the in-canon problems of Iron Man 2 facilitated a quick course correction, making a clean break from the dodgy explanation that Tony created it before the nascent MCU became too complicated to undo it. The vibranium retcon in Captain America might have been made without knowing when or if Wakanda would play a role in future movies. But comic book writers of all stripes often leave such Easter eggs in place, and the MCU has followed their example many times. Keeping vibranium in Stark’s stable would focus the universe too much on one character, whereas opening it up -- even if the filmmakers didn’t know where it might lead -- provided options to expand the MCU beyond him.