MLAUGHLINNYC, I went onto Olsen’s, and checked each CD, for content. If you already own a Postwar Repair Manual, The CD-PRE would be a compliment for Prewar @ $35+. For anyone that doesn’t have Postwar coverage, the CD4-1 is the better buy, @ $50+, which is basically a complete reprint of their Library, covering Pre/Postwar Lionel, Marx, some AF, & Dorfan, which is what you see when entering their Library.
The CD-POST=$35; CD-PRE=$35; CD4.1=$50+, so the $50 value is best, if both Pre/Postwar are needed.