Navigation - C-Nav or D-nav in 2000 S500?

While looking on eBay for a replacement navigation CD for a 2000 S500 I'm buying, I was informed that this model year was initially equipped with C-Nav systems, and D-Nav systems were installed later in the year.
I need to figure out which one my car has so I get a compatible CD - anyone know how I determine this, short of contacting the original dealer?
Thanks! Dev

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