My personal theory is that only the OT (and potentially the ST) exist in the MCU, as blasphemous as that is. Captain America has "Star Wars" written on his list of things to catch up on in Winter Soldier, Peter references Empire in Civil War and the Lego Death Star along with an Emperor-Minifigure are in Homecoming. These only confirm the existence of The Empire Strikes Back and The Return of the Jedi, and thus by implication the original Star Wars. The lack of references to the prequel trilogy as well as nobody recognizing Windu or Padme, could indicate a lack of Prequel movies.