There were at least 4-5 cars to start. 1 'Hero' car that Hoff drove, 1 Camera car that was used specifically for the trailer sequences, a 3rd 'Stunt' car modified w/ only a roll bar, a 'Jump' car which was was really just a shell and a 'Robot' car that had the modified driving controls in the backseat w/ a tarp to hide the driver. Some say that the 'Hero' car Hoff drove had the backseat controls, so there were only 4 cars when they started.
More were made throughout the show and the 4th and final season had 4 more KITT's created for his super pursuit mode and convertible modes. The convertible mode never drove, it was towed in all sequences
The Hoff sold his car, but over time after the show was over, KITT would still show up with him at various events and, well, music videos.
https://youtube.com/watch?v=RE4k-eOOxaE