Well, these microswitches are not only simple switches. They also carry 2 resistors internally, one in a row, the 2nd in parallel.
It's not a simple switch, there is always a current flow between the 2 wires of a microswitch. That's why you can diagnose it with an ohm meter: 570 ohms vs 2.770 ohms are the standard values.
The Cabrio Top Module (CTM) always checks the presence of all sensors as well as of all actors. If a wire is broken the CTM can identify it. If there is a short between 2 sensor wires , it can be detected as well. In addition, the 2 states OPEN as well as CLOSED.
The problem over the years arises by corrosion inside of the switches. Depending on the weather, the humidity inside of these microswitches can differ: the one day it works fine, the other not.