After reading this question, I suddenly wondered if there is any existing material within the MCU that explains how Thanos came by the Mind Stone in order to then give it to Loki to try and gain the Space Stone.
Did he create the Sceptre and place the Mind Stone inside it, or did he locate it and it was already in there?
I'm aware that none of the movies themselves directly mention this, but I am wondering if the Avengers directors (Joss Whedon or the Russo brothers) have ever explained just how he came to be in possession of the first of the 6 Infinity Stones?
Or perhaps there was some preview comic released that addressed this?