According to the technician I spoke with, he could only detect three on their end.

The cable was chewed through by cats, so perhaps it was three just in that moment.

The connection was overall unreliable, so I guess it must have been four, just not all of the time.

There is two wire ethernet that supports 100. It isn't common, but automotive is starting to use it.

3 pairs probably. But then again you only need 2.