Nav system is reporting randomly wrong data for number of stalls free for the past few weeks. Today it was reporting 4 free stalls (out of 6) and when I got there, no stalls were occupied. When I plugged in, it reported just one free stall (still nobody there) and after I unplugged it went back to 4 free stalls. Same at other times for the past few weeks. All of the stalls seem to be working... just incorrect reporting.
So... don't trust the nav system. It's wrong.