Actually, there were TWO "specials" in those times. The "Spring Special" related to some new colors and possibly upgraded options on the normal cars, designed to give the populace a reason to come into the show rooms after winter and the holiday seasons.
Then, a month or so later, the "Sales Special" promotions appeared. Which would be the cars with "Free Automatic Transmissions" or "Free Air Conditioning", which were reflected on the MSRP sticker. In addition, there usually were some slightly different pairings of items which were available as individual options in to a special option group AND usually some sort of normal color. As vehicles as the Dodge "White Hat Specials" or similar Plymouth Furys. For example, the 1966 Fury IIIs were all silver four-door sedans (or at least that was what the local C -P -I dealer ordered).
The "Sales Specials", with their dedicated color and trim, gave the customer something they could point to and say "I got a nice car for less money" sort of thing. But for the "free automatic transmission" cars, no special trims, just the 'money-saving deals" on the window sticker.
Having TWO levels of "specials" might explain some of the inconsistencies noted. At least that's what I recall seeing in the pre-1972 times before I went off to my last four years of college in a larger town 4 hours away. During those pre-1972 times, I was in and out of the local dealership getting our cars serviced and taken care of. While there, I would talk to one of the salepeople and look at the cars on the lot window stickers. Plus noticing the ads in the local and regional newspapers where the "Sales Specials" were promoted.
Between the first appearance of the "Spring Specials" after the first of the calendar years, followed by the "Sales Specials" in about March, that could give the dealers about 6 months of having good sales traffic before things started to wind-down for "Build Out" in the late summer. To prepare for the new model year getting ready to happen in Sept-Oct times.
Just what I observed locally and regionally, being in "The Dallas Zone" of things.
Now, all of these things in Chrysler Corp can or should be noted on the Build Sheet and/or Data Plate.
Starting in about 1973, a group of Dallas area Oldsmobile dealers got together and wanted a car between the basic Cutlass "S" and the Cutlass Supreme. They made a deal with GM/Olds to install the Cutlass Supreme front clip sheet metal on the normal Cutlass "S" body, then with a little nicer interior trim. The cars looked like a Cutlass Supreme but did not say "Supreme" on them anywhere, with a VIN that was "Cutlass". These cars were only produced, or started out that way, for the spring selling season, with many ads proclaiming these special cars. In order to get these cars, the dealer group had to order something like 2000 of them as a group. This deal went on for about three model years, until the body style changed.
As NONE of this was documented in the parts book, the local Olds parts people had to be on top of things, to ask questions about the "Cutlass" cars the body shop customers needed front end sheet metal. Additionally, back then, the front of the GM store did not talk to the back of the GM store, except in some unusual cases, plus that nobody in GM worried or knew about "Build Sheets" back then, there could be some tense moments iin getting things figured out. "Those things" were only in the realm of Corvette owners and such, back then.
Just my observations from back then,
CBODY67