I've heard back from U.S. cachers VWjunkies. They were a couple who cached together but have split, their Geocaching.com account being retained by the female half, Knockout Ferrari being taken by her former partner and passed onto an unknown Florida-based cacher, which is where the trail goes cold; therefore I've marked KF as "whereabouts unknown".
Smart451's Smart Car 10 Knockout Racer TB was retrieved yesterday by German cachers Ilmaran, who promptly placed it into this puzzle-cache dedicated to the 20th anniversary of the fall of The Berlin Wall, adding 8.58 miles to it's distance travelled.
Also adding a little distance to it's total milage travelled (although still the most vulnerable to elimination from the Knockout) is Mat Smith's Hazards of Geocaching 2 (The Sheep) John's Knockout Racer TB, which was dropped into this typically-Dutch multicache, 18.1 miles from the last cache that it visited.
Scroll to bottom of this page for current official Knockout placings