I've been there in a previous car with dashcams. Sadly, reading number plates under night conditions basically isn't going to happen on any consumer-grade DVR setup, especially on cars going the other way. Although your eyes allow you to read them, cameras just aren't anywhere near as good at low-light resolution. There's normally either not enough light, or way too much light from your headlights on the plates visible from the front camera, and at the rear it's more like there's either no light at all, or the headlights of the car behind blind the camera to anything else. Stationary in a queue of cars is about the only time you're going to get legible number plates at night, and even then your brake lights need to be on to throw some light onto the plate of the car behind you.