David
The Lionel thinking back around the 90s I believe was that not everyone who bought the initial set would be a customer for add ons . In the case of the Madison cars the add on was the Madison baggage car and we know that Lionel misjudged the demand for this one. The same was true with the add on B unit for the Santa Fe F-3 ABA Streamliner set from about the same time period. Lionel took up the idea of the add on to sets to spur collector interest in its products as a big part of its market appeal were toy train collectors .
The Phenolic cars are quite interesting . They are scale dimensioned and were made pretty much as they might have been in the 1940s .What makes them "semi-scale" so to speak is that they were equipped with the deep flange trucks and lionel "claw" couplers rather than scale wheels and couplers. That was how Lionel denoted the difference back in 1941 for the product produced at that time.The 1991 catalog that showed those Madisons and the phenolic cars picturing them with the 1-700E Hudson and the Scale B-6 switcher. These were the most advanced lionel sets in the 1941 catalog from 50 years earlier. The Madison cars from 1991 are very similar in color to the prewar cars , more brown than the maroon or tuscan cars released in the postwar years. The stock car and Refrigerator car produced shortly after the release of the phenolics in 1991 have always interested me as I wondered if they were made from tooling that may have existed back in 1941. The war would have precluded their release and in the immediate postwar period, these sets were maybe contemplated by Lionel but never made.