Your vehicle’s traveling speed and the other vehicle's speed play an important role in your dash cam’s license plate readability. Going back to the 1080p Full HD dash cam - yes, it records in Full HD, but only when it’s a still picture. Motion changes everything.
If your vehicle travels much faster or slower than the other vehicle, chances are your dash cam will not be able to pick up all the license plate numbers and details. Most dash cams on the market shoot at 30FPS, and a speed differential greater than 10 mph would likely result in blurry details. It’s not your dash cam’s fault, it’s just physics.
That being said, if there was some point where you were traveling at the same speed as the other vehicle, you might be able to get a good view of the license plate in your video footage.