In the original Star Wars (1977), the following conversation happens near the end of the first scene after the Star Destroyer Devastator captures Tantive IV and Darth Vader—and his troops—have boarded the captured ship looking for the stolen Death Star plans:
Another Imperial Officer approaches Vader and the Commander. They stop and snap to attention.
Lord Vader, the battle station plans are not aboard this ship! And no transmissions were made. An escape pod was jettisoned during the fighting, but no life forms were aboard.
Vader turns to the Commander.
She must have hidden the plans in the escape pod. Send a detachment down to retrieve them. See to it personally, Commander. There’ll be no one to stop us this time.
Given that Rogue One (2016) now attempts to retcon the whole backstory of, “…Rebel spies managed to steal secret plans to the Empire’s ultimate weapon, the Death Star…” is there some explanation/clarification (official Disney canon or “Legends”) as to who or what has has ever somehow stood in the way of Darth Vader (or the Empire) in the past before any of these specific events depicted in the original Star Wars (1977)?
PS: Yes, I am well aware that Rogue One (2016) is considered official canon, but adding “Legends” just in case something there hints at something that might not be explicitly addressed elsewhere.