Maybe they weren't a late year promotion. But,that is what I have always understood,that they did them to help sell off these trucks to make way for the new-style '73. Makes sense to me,who would want a '73 if there were still beautiful '72s on the lot?
Just kidding,I like those trucks,too. And actually,the mentality was "go with the new look" back then. I had so many say to me how they had to have the new style and now (then) regret getting rid of their '72. My first truck was a Highlander off the OK lot in '73. The truck was like new,not a scratch in the bed. Can't recall the mileage,but it was under 10,000. I always figured it was traded in because the p.o. just had to have the "new look". Maybe it was because they came out with the 454. I'm pretty sure whoever ordered my truck was a motorhead.
Anyway,I never paid attention to numbers. If your truck is down that low the Highlanders must have been made all year,or most of it. Basically,the Highlander package was the pilot for things to come with packaging options as the savings. One more reason I look at these trucks as the last of the old and the first of the new. The transition from good old trucks to what they have become today.