When researching or admiring a classic car do your homework.
You will probably notice right away that all tags have some differences, subtle and otherwise. The purpose if this tool is to assist people like you in decoding all of the letters and numbers to figure out what General Motors is telling you about the car by where is was built, when, what color it was originally, accessories and whatnot. One question that comes up in many forums is; "Why are there so many differences?" My instance response is to say "Ask GM" and I have never found a good explaintion as to 'why' Fremont, CA did is differently than Pontiac, MI. That being said, we have made every effort to take into account as many variables as possible between all GM assembly plants over the years. GM finally did something right by standardizing most tag design and codes around 1969-70 so that makes it easier decode tags from that point forward.
The following is a guideline for what data the tags have.
TIME BUILT CODE: The date of manufacture of the car. Consisting of 2 numbers and 1 letter, the code tells you the month and week of the month the car was built. The 2 digits represent the month (01=January, 02=Feburary, etc.) while the letter represents the week of the month (A=1st week, B=2nd week, etc.). It’s not possible to pinpoint a specific day of manufacture from the data plate, only the week of the month the car was built can be determined. Generally, most date-coded components on the car were built between 2 and 8 weeks before the build date of the car. There are, however, exceptions to this rule.
MODEL YEAR: To the right of the “ST” letters (short for “Style”) are the last 2 digits of the model year of the car. “64″=1964, “70″=1970, etc.
DIVISION SERIES: The first digit of this code identifies the GM division (1=Chevrolet, 2=Pontiac, 3=Oldsmobile, 4=Buick), the second and third digits identify the series (Chevelle, LeMans, Cutlass, Skylark, etc.). While the series code on the data plate may not match the series code in the V.I.N., it must be from the same family (the series code will not represent an Impala on a Chevelle data plate, or a Catalina on a LeMans plate, and so on).
BODY TYPE: Following the division series is a 3 or 4-digit code that identifies the body style (or type) of the car, such as 2-door coupe, 2-door convertible, 4-door sedan, etc. Most 3-digit body type codes were from 1964 and earlier.
ASSEMBLY PLANT: This code identifies the assembly plant where the body was mated to the chassis/driveline, and final assembly procedures were performed. This is a 1 to 3 character code, and it must match the assembly plant code in the V.I.N.
UNIT NUMBER: To the left or the right of the BODY or BDY letters is the unit number assigned at Fisher Body. This number will not match any numbers in the V.I.N. and is not significant to identification or restoration purposes.
TRIM NUMBER: To the right of the TR letters (short for TRIM) is the interior code. This 3-digit code shows the color and style of the interior and seats.
BODY COLOR: To the left or the right of the PAINT or PNT letters are the exterior color codes. On 1964 Chevrolets, the codes are all 3 digits (including two-tone cars, which have unique 3-digit codes). From 1965 to mid-1969, Chevrolet used 2 letters–the first is for the lower body color and the second is for the roof paint, vinyl top or convertible top color. Buick, Olds and Pontiac used this 2-letter system from 1964 to mid-1969. From mid-1969 to 1972, all divisions used a 2-digit code for the lower color, followed by a 2-digit code for the roof paint, or a letter for the vinyl roof or convertible top color.
Also there are some instances where the wheel color is included in the paint line and is charactized with a thrid code at the end of the upper and lower body color. This does not appear often, but there are examples out there.
ACCESSORY CODES: On 1967-and-earlier models only, there may be accessory codes listed on the data plate. These codes indicate certain options on the car. Some of these codes have been decoded on Chevrolet and Pontiac vehicles, while Buick and Olds are still a mystery. The following types of equipment have been listed on data plates that have been decoded: tinted glass, transmission, console, air conditioning, radio, mirrors, rear defroster, seat belts, and bumper guards. These codes can appear either in a straight line of codes or stacked into two lines.
These codes will not appear on most 1968-and-later plates. The only exception is Cadillac which continued to use accessory codes using a slightly different layout on the tag. For other tags, accessory codes reappear with a different format and unified coding system called Regular Production Codes (often called RPO Codes) in 1970 on various cars.
SEAT TYPE: There may or may not be an additional code following the trim code that identifies the type of seat installed in the car.
TOP: On some tags might have a line, often on the bottom left saying TOP. This defined what color a convertible top was when the car was assembled.