Well the AHM/Rivarossi cars started being produced in the 1960s, the IHC cars came along in the 1990s, so it’s unlikely some third party created the molds and sold them to the two companies 30 years apart. The cars are similar except for all the differences you note - ends are different, one has cast on handrails, other has holes for add-on parts, etc.
Since the two companies cars overlap by 10 years or so, I find it hard to believe Rivarossi sold or leased their molds to another company so that company could make a competing copy to sell. IIRC the IHC cars were manufactured in Yugoslavia (by Mehano?). They maybe just tried to do a ‘knock-off’ version of the popular Rivarossi cars, making them different enough that Rivarossi couldn’t successfully sue them.
It’s the same car with IHC adding additional details. I don’t know enough about the mold making process to know if a mold can be created from the various parts or what it would take to duplicate a mold and then make modifications but there is no question that these cars had the same origin. The IHC car is not inferior to the Rivarossi car. 98% of it is identical in every way and IHC made a few minor enhancements. Every car I’ve seen sold under the IHC name I instantly recognized as a Rivarossi car. Same body, same underside, same trucks, even the same oversized flanges on the plastic wheels.
I found this thread from 2004 in which a poster explains that when AHM went belly up, they reorganized as IHC with the same address and continued to market Rivarossi equipment. Later IHC and Rivarossi had a falling out and IHC turned to other manufacturers so maybe those are the cars you are thinking of that were inferior to the Rivarossi cars.
IHC Vs Rivarossi - Model Railroader Magazine - Model Railroading, Model Trains, Reviews, Track Plans, and Forums
I think what appear to be louvered windows on your models are actually molded on representations of the steel bars that covered the windows of most RPOs I’ve ever seen. This is one of the “joys” of molded on detail.
MECman,
If you wish to acquire the entire 20 plus year run of Mainline Modeler magazine on a single CD, the Chesapeake and Ohio Historical Society (www.cohs.org) has the entire collection from the first issue in 1980 to the very last, available. Well worth the price if, prototypical accuracy, and how to achieve it, is important to you.