There is quite a broad range of rolling stock that would be appropriate to the period. Just a few of these are many 36', 40' and 50' single and double sheathed, plus X-29, 1937 and 40's AAR design steel boxcars. A great many all steel open hoppers lasted decades, along with war emergency wood and steel open hoppers not yet rebuilt following the war. Ice reefers were still common and the selection of 40' tank cars almost limitless. Most any car with a post-WWI built date was possible in the 40's and even well into the 50's in some cases. Check the tiny BUILT (BLT.) and NEW dates on the model to see when the car was first in-service. If it is prior to the supposed date on your RR, then it's likely to be OK.
The bigger concern is identifying whether the car's paint scheme and lettering are appropriate to the date you choose for your layout. Prior to WWII most railroads retained the same mainly bland paint schemes (other than for billboard reefers), heralds and lettering for many years. After the war things quickly began to change, in some cases with designs being altered completely every few years. The big stumbling block with modeling is that very few manufacturers indicate exactly what interval of years the paint scheme on their cars corresponds to. Thus, while a double sheathed freight car may have a built data of 1939, the way its painted up may only be appropriate for that given RR in post 1955, when the car would be on its last legs.
All too often manufacturers have also included bogus paint schemes various cars never ever had, particularly in regard to HO and N scale models manufactured before 2000. So, if you really want your trains to look correct to the period your layout represents, it is going to take some reseaching of vintage photos to identify what paint and lettering schemes were in use at the time.
NYW&B