UPDATE: Confirmed! It's real! See ayumi's lsusb dump: https://transfem.social/notes/a9j1rc059tdj0vpx
Today in vendors slipping single bits (or single bit!) of information into weird places:
I am *completely* certain that Google once made a USB-C audio adapter that has a *different USB PID* depending on whether it has something plugged into it.
I am somewhat certain that it's 18d1:5025 with something plugged in, and 18d1:5029 without.