Start a GTA VI traffic notebook from the launch trailer
Pause on a frame where a vehicle is clear and write down the timestamp, body shape and camera angle. If several cars share the shot, identify yours by its position in the frame. That gives someone else a chance to find the same vehicle without interpreting your screenshot first.
Leave an empty field for the in-game model name. When you can confirm it later, keep the old note and add the evidence that settled it. The record will show which parts were observable in the trailer and which came from playing.