Lighter

The two concepts "where it physically is " and "how likely I am to find it" seem to be sufficiently distinct.

Quite right but that isn't what you said that reduced me to tears. What you said (with my emphasis) was

The key is that there's a distinction between the odds of where the car *is* (1 in 2 for either of the two final doors, regardless)

AND

the odds that you, the contestant, will *find* the car.

Physically, the car is behind one, and only one, of the doors. It is not fifty percent behind one and fifty percent behind the other. The trouble is, we don't know which. That's where the odds come in. From the information available, we can calculate the probabilities. For your late comer, there are two doors with a car behind one and a goat behind the other so the 50:50 option is the best he can do. But, we have more information than that so, if we analyse it properly, we can calculate more accurate probabilities. In this case, that the odds are 1/3 for the door the contestant chose and 2/3 for the one that Monty didn't open. The 50:50 odds have now gone.

In the first part of your distinction above, you seem to think that the odds have some sort of physical reality. They do not. They only exist in our heads as a result of the analysis we have made of the information.

As a bit of an aside. It might help you to think, not of the door that Monty chose to open, but of the one he chose not to open. In two situations out of three, depending on the contestants first choice, he chose not to open it because it had the car behind it.