Mazda B-4000 radio

I have a Mazda B-4000 with an AM/FM/CD player, The controls on the
radio do not match the controls shown in the owner's manual.

The manual shows two rocker switches: Seek and Tune, They are for
changing channels on the radio. My Tune button is labelled Tune/Discs.
If I press it while in CD mode, the letter "C" appears on the display,
but nothing seems to change. Pressing it again does not remove the
"C."

Also, my preset radio buttons 1 and 2 have additional labels:

<< CD and >>CD.

They don't seem to do anything either (in CD mode).

It almost looks like the radio is built to accomodate a multiple CD
changer, but there is no mention of such in the manual.

Any ideas?

Dick Evans