Steve,
The curly cue couplers were featured on the 9.5 inch cars only in 1938 and then on the 6 inch cars only in 1939.
The earliest cars from 1938 had very thin couplers.
This green tank on green frame tank car variation has the thin/short-height couplers
This searchlight car has the thicker/tall-height curly cue coupler
As for you missing anything, I would say only color variations.
This boxcar has evidence of being a 1937 variation that had the 1937 couplers and trucks pried off at the factory and replaced with 1938 trucks and couplers. This process has been noted in the Greenberg's Guide and is the first and only car like it that I have observed. Note it has the earlier cream color instead of the later more orange color and again note the thin/short-height coupler.
A green tank on blue frame tank car variation
There is also the orange log car.
NWL
