These kind of car specific speed restrictions, when contained in a train, would likely have been in special notices ("pink" sheets IIRC?) and/or special instructions. Some of the later restrictions we operated under, for things like the empty bulkhead flats, when they discovered the stability problems running empty, (but not loaded-no restrictions), or (IIRC???) some of the early speed restrictions on hazardous commodities were in bulletins, or special notices, or special instructions.