"SO NUMBER" The Shipping Order or Sequence Order Number is the estimated day and order the car was scheduled to come down the assembly line. It consists of a three character number followed by a six digit number. The first three will be a letter/number combination or all three will be numbers. This will give the approximate build date of the car.
If there is a number for the first digit, then that is the month, 1 = January, 2 = February, etc.....If it’s a letter for the first digit, then letters are for the last months of the year. A = October, B = November, C = December.
So A11 would be October 11th, and 502 would be May 2nd. The other 5 mean nothing as far as the car is concerned, it’s only a random number and doesn’t decode anything.
504 = May 4, 1965
914 = Sept 14 1964 (early build date for a '65)
The SO number, later Vehicle Order Number VON, is a unique identifying number assigned to a vehicle before the VIN is assigned. It is the primary number used to order a car and for corporate to invoice the dealer and tracking the build. It's found on the Broadcast sheet, IBM card when applicable, shipping invoices, car invoice, window sticker and probably a couple of other places. There are many nuances and differences per year but generally for the years 1961-1979:
The whole SO number contains the scheduled production date (SPD) and a four to six digit identifying number.
The date format varies by year.
64 and earlier use a four digit date code where the month is also a number. So an SPD of 1115 indicating November 15th exists.
65 is the first year to use letters for Oct, Nov, Dec.
One way to help identify the model year of tags:
64 and earlier use a four digit date and a four digit vehicle identifier
65, 66 and 67 use a three digit date code and five digits. Model year 1968 is the first year to use a six character identifying number.
Pre 68...the cheapest lines have the lowest first digits escalating in price class to the Imperial. e.g. Valiants and Barracudas SO numbers start with 00, while the Imperial line will start with, say, 14. The B and C bodys will fall in between like 04, 06, 08. This applies to ordinary cars. Fleet, lease, special order et al cars have also have specialty first numbers......