Something I've stored on how to tell Athearn cars from All-Nation (from J. Pantry).
In addition to this information, the materials that were used varied widely, ranging from stamped tin plated steel, to brass, to aluminum. The last couple of Athearn kits that I got while that line was held by Jan Lorenzen of LWS were a mix of materials. Most were brass after that line moved to Beat Hug's ownership under the Old Pullman label.
The following are the spotting features between All-Nation and Athearn.
How to tell whether a 40' steel sided boxcar (with metal roof, metal ends, and metal underframe) is an Athearn car or an All-Nation car:
1) If you measure the length of the car from the underside, from the inside of one metal end to the inside of the other metal end, an All-Nation car will measure 10", whereas an Athearn car will measure 10-1/8". This is the same dimension as the car sides.
2) If you open the doors, an Athearn car will have a wood or composition inner wall, whereas an All-Nation car will not.
3) Just below the right end of the lower door slide, the scalloped edge along the bottom of the car side, an All-Nation car will be cut vertically, whereas an Athearn car will be cut at an angle, just like all of the other scalloped edges on both cars. Obviously, a modeler could trim an All-Nation car to look like an Athearn, but an Athearn car would never be made to look like an All-Nation.
4) Along the bottom edge of the roof overhang, along the side of the car, most Athearn cars will have a row of rivets, whereas an All-Nation car will not. Do not confuse this row of rivets with the row of rivets along the top edge of the car side, which both cars have.
There are other more subtle differences between the two, but the above differences will enable you to determine which it is. I avoid ends, doors, and underframes in my comparison because those items are easily interchanged between the two.
How to tell whether other car types are Athearn or All-Nation:
Athearn had a 50' steel sided boxcar (with metal roof, metal ends, and metal underframe). All-Nation did not.
Athearn had a 40' steel sided reefer (with metal roof, metal ends, and metal underframe). All-Nation did not.
All-Nation had a 36', 40', and 50' wood sided reefer (with wood roof, wood ends, and wood underframe). Athearn did not.
All-Nation had a 40' wood sided reefer (with metal roof, metal ends, and metal underframe). Athearn did not.
All-Nation had a 40' outside braced boxcar (with wood roof, metal ends, and metal underframe). Athearn did not.
Both All-Nation and Athearn had a 40' wood sided boxcar (with metal roof, metal ends, and metal underframe). However, the above 1st and 4th rules still apply.
Athearn also had a few one-of-a-kind cars that do not follow all of the rules of their other 40' steel sided boxcars. The Rock Island 20060 aluminum boxcar is one of those exceptions. There was also a GN 2500 aluminum boxcar, a GN 44424 orange sided boxcar, and a GN 47872 wood sided boxcar.