If you are down 4 touchdowns, your odds of winning are probably less than 1%.
If you then score three touchdowns, your odds will have increased dramatically. That Diane mean the initial odds of less than 1% were incorrect. The situation changed.
Same thing with the problem we are mulling over... With the initial 3 doors you have a 1/3 chance.
Once they reveal an incorrect option for for you, your odds change to 1/2. This doesn't mean your initial odds were incorrect, merely that the situation changed.
The metaphorical scoring of three touchdowns.