I've read the concept that a self driving car cannot react to everything that it sees in front of it because otherwise it would basically be inoperable, ie, it

I've read the concept that a self driving car cannot react to everything that it sees in front of it because otherwise it would basically be inoperable, ie, it has to disregard things like overhead signs, bridges crossing over the highway etc, because braking for those is unnecessary and possibly dangerous. But, when the car detects these things and decides to disregard them, does it just forget about them? Just thinking back to the Tesla car that ended up going under the truck crossing in its path, supposedly the car didn't react as you would expect because it assumed it was an overhead sign. But I would think that an overhead sign would begin to look different than a truck on the road crossing in front of you as you continue to get closer to it, is the software not capable of at first deciding to disregard something up ahead but then change its mind as it gets closer? Likewise with a concrete stanchion that keeps getting closer and closer? Does the software allow for it to second guess itself?