For whatever reason on the east coast we've always used the terms in the opposite orientation. ;)
DNF = never crossed the finish line
Off Course = got lost or missed a gate
Apparently your club never had the dis-pleasure of using AXware! When I started out here in the northeast, O/C (arms crossed over the courseworker's head) meant that the driver missed a gate. DNF meant that they had a major problem on the course and either exited prematurely or were towed off without tripping the timer. Pre-computer paper timing cards used this convention, as did the early spreadsheet scoring system developed/shared by a club in CT and even the SCCA National Office's TS98x package.
In AXware, Vitek's definitions were backwards. His idea of a DNF (X on keyboard) was a car that missed a gate, and Off Course (O on keyboard) was for a car that did not trip the finish lights. (O also stops the running time for the car!) I argued until I was blue in the face that it should be the other way, but he never changed it. AXware allowed you change the labels/keys for the two functions, but I gave up the fight after a few years because we couldn't borrow computer operators from neighboring regions without losing times (via O) since they all used the default AXware settings.
It appears that Pronto T&S picked up on the AXware standard, and perusing last year's Nationals results on the SCCA web site reveals that they just post "DNF" with no time in the results.
Long story short, I 100% agree with @Duke in the meanings of DNF versus O/C, but the "backwards" standard is apparently nation-wide now.....
Cat herder emeritus - Poughkeepsie Sports Car Club, Inc
Solo Chair (retired) - New York Region, SCCA
AXti.me user since June 28, 2015