In the "FSD Preview" update that came out around Christmas time, the car now shows a bunch of symbols on the road, and signs (aka stop signs) that it recognizes. They don't flicker at all, even while you're driving and a large truck obscures the car's vision of the sign / stoplight. So they likely have started to enable some form of temporal memory into the system so that it remembers what it has observed in the environment both frame-to-frame and overall.
That hasn't been my experience. The visualization only ever shows what I can see with my own eyes, and the cameras are in a very similar position. I've definitely watched traffic signals come and go, all while not moving an inch.
