Pin numbers of the terminal blocks are not the same as the Arduino pin numbers! The pinout diagram at https://content.arduino.cc/assets/Pinout-UNOrev3_latest.pdf shows:
And you can see that the pin marked as A1 is also D15, but the silkscreen on the board only shows it as A1. In the IDE A1 is defined to be 15, so it doesn't matter which you use
Now if you look at the schematic:
You see that net AD1 connects to ADC1, which is Port C bit 1 in the ATmega328P microcontroller and connects to pin 2 of the terminal block AD. Sadly, we can't tell the pin ordering of the terminal block AD or even where AD is from any of the above screen snaps! We just have to rely on the schematic matching the board, which is fairly safe bet on such an old product with lots of sales.