My understanding is that National Car Company was Fruit Grower’s answer for meat reefers. Wikipedia states: In February, 1928 FGE formed the National Car Company as a subsidiary to service the meat transportation market.
All photos I have of NX cars are leased to meat packers, or marked with meat rails for meat service. A photo of NX 3647 shows a wood sided reefer with metal running board (long rectangle pattern), and a lighter colored roof (BW photo). The car is lettered to be returned to CBQ at Galesburg and was weighed at PLT, ie Plattsmouth. Morrel, Kahns, & Rath used NX reefers.
Protocraft’s website offers this.
The National Car Company was established in 1930 as a leasing subsidiary of the FGE. By 1940, NX had more than 1,600 reefers on its roster with many other
reporting marks for their leased cars such as Oscar Mayer (OMX), Kingan & CO. (KRLX), E. Kahn (EKSX), Superior Packing (SPCX) and others. National operated
into the 1960’s. Cars with the NX reporting marks were leased to the other company’s and railroads with signs on the side directing it’s return to the lessee.