The Decoder Source Book was a non-glossy black and white insert which I first encountered in the March 1991 issue of 'MorPerformance For The Chrysler Enthusiast'.
That magazine changed titles several times during publication and by the December 1996 issue had been become 'Chrysler Car Enthusiast Engines etc'. That issue only contained articles about codes; Date, Option, Engine, Drivetrain and much more including the Decoder Source Book which is included as one of the articles, this time on glossy paper. It even had a little chart breaking down the Body Designation of A - P body cars.
That was the second time I came across the Decoder Source Book. Personally, I haven't seen a magazine cram so much info in less than 70 pages of one single issue. If there is one book or mag for anyone to pore over to simply just learn, then that issue would be it.