FWIW, here's a selection of ISO container codes:
1984 L(ft) H(ft) Characteristics
4000 40 8 Opening(s) at one end or both ends
4020 40 8 Insulated/vented
4300 40 8.6 Opening(s) at one end or both ends
4301 40 8.6 Dry Van
4305 40 8.6 Dry Van
4320 40 8.6 Insulated/vented
4400 40 9 Dry Van
4420 40 9 Insulated/vented
4426 40 9 Insulated/vented
4500 40 9.6 Opening(s) at one end or both ends
4510 40 9.6 Passive vents at upper part of cargo space
4511 40 9.6 Dry Van
4550 40 9.6 Opening(s) at one or both ends
So as you can see, 40' containers were common enough in 8', 8'6", 9', 9'6" heights prior to 1995 to have their own ISO codes.
So it's not necessarily that the Athearn 9' height is wrong, from a decoration paint of view it should probably have a 4400 ISO code.