I had the same thought -- but was surprised the Tesla reads signs as opposed to what Waze does, which is use maps. But the Tesla has the advantage it would work outside of network.
BUT -- context is everything! If you saw an 85mph zone in a residential area or school zone -- you'd know it was bogus because you're a human and it doesn't seem reasonable.
https://www.gwinnettdailypost.com/local/cities/johnscreek/jo...