Sorting out option codes on glovebox sticker?

[williso]

HI,
I've been looking at these for awhile, both on trucks I've seen locally and when people post pics of their option sheets, and like everybody else I've noticed that sometimes the codes are just 3 digits (for example C42 = heater) and sometimes they are 5 or 6 digits (for example C42AC = heater or 1C42AC = heater).

Anyway I've been trying to see if there was any pattern as to when the 3 digit vs 5 digit codes were used. Not too much luck so far, apart from seeing that it doesn't seem to be a Chevy vs GMC thing, and not a year-to-year thing either (I've seen 1972's with 3 digits and 1972's with 5 or 6 digits).

So far the only thing I've turned up that might explain it is the assembly plant. To be specific, every Flint , Tareytown, Atlanta, and St. Louis truck I've seen had 5 or 6 digits, while every Fremont or Baltimore truck had 3.

But I haven't seen all that many trucks overall, so I can't be sure if that's the real explanation or not. Anybody willing to look at their option sheets and post what plant their truck came from and what their option #'s look like so we can maybe figure this thing out?