I love how Beyonce isn't in any of this.
It's obvious that Gaga's version had original vocals from her that was sent to Britney. Britney recorded the rest but shelved it because of phonography and no one knew who was Gaga back then. After she became popular Britney wanted it for her singles collection, but Gaga already got Beyonce for it for her own album and didn't want to give it away.