I have eliminated the possibility of the a/c drain, not only because the technician checked it, but also because I ran the defroster for 30 minutes, then the a/c for 30 minutes, and I saw a nice, normal puddle of condensation under my car.
The windshield is OEM Ford Carlite.
The car was a 3-year lease return when we got it, and it had 29K miles on it. I cannot say for sure if the windshield was ever replaced during the first three years of its life, but if it was, it was replaced with a Ford windshield.