Agreed. If they had instead shown a Rebel trooper frantically transmitting the plans to a nearby system (before being killed by Vader, of course), and Vader's ship then preparing to go to that system, her claim of innocence would have made a bit more sense. Instead they have some incredibly concrete evidence that Leia's ship was indeed there and had just escaped from under Vader's nose.
Given that A New Hope doesn't (presumably) start in the same star system, it actually feels pretty reasonable to me. The Tantive IV made a couple hyperspace jumps, Vader followed on his Star Destroyer, but their only concrete evidence was that it was a Corellian corvette of similar appearance to the one which escaped the battle. If the "diplomatic mission" excuse had been something more than what Leia cooked up on the spot, you'd think that they'd have been aboard a ship that wasn't full of soldiers in Alliance uniform. If it had been a real cover, they would have been kitted out for an actual diplomatic mission, with the plans in a well-concealed hidey-hole, and allowed boarding without resistance.
The entire opening sequence of Episode IV positively reeks of desperation and a plan cobbled together on the spot. Likely Leia recorded her message for Obi-Wan in however many minutes or hours passed between their escape and boarding.
Hmm. Never really thought of it that way. A New Hope certainly starts in a different system, which means that the Tantive IV made at least one jump; probably multiple jumps to try and shake pursuit.
One very minor point of contention though: I'm not certain that the Rebels had what could be called a uniform at that point. The raiding commandos sure didn't seem to have anything of the sort, at least as far as I can remember. It's more likely that the troopers we see near the end of Rogue One and the beginning of ANH are at least nominally members of a different unit, perhaps Alderannian Royal Guards of some kind, or Senate Guards (the Senate did still exist at the beginning of ANH, if only as a sort of puppet government). I don't have any real proof and canon might disagree with me on this, but the fact that their uniforms and equipment were so unlike the hodgepodge gear the rest of the Rebels used makes me wonder.
