Well, hyperspace tracking only became a thing in TLJ. I think that’d make RO and ANH a few days apart. Not only that, but Vader never knew if Leia was on board or not.
Likely did since it’s a consular ship, from the registry they know the planet and he’s looking for the ambassador. Which then raises the question of why use such a recognizable ship for a covert mission. Actually, it brings me to mind the Snowden debacle. The US forced down a consulate aircraft under suspicion that Snowden was onboard and should have been a bigger international incident than it was. You simply don’t do this. Given that they were operating under some of the last traditions of the Old Republic, perhaps it was a bluff they thought they could pull off.