EAD DSP-7000 III- INV switch function?

I currently own an EAD DSP-7000 MkIII DAC. It has Series III faceplate and HDCD plaque over the de-emphasis lamp.
Does the INV (invert polarity) switch function on this model? I have tried this switch on about 30 CDs and can't hear any difference.
Thanks for any info.
maybe it's not functioning. You should hear some change definitely if it's working right. The III I previously owned the switch definitely functioned.