Not all were impacted by the ICC ruling, just a lot of restrictions put on them. The ruling did not affect privately owned reefers and they can still advertise to this day. What hurt the billboard reefer in the rule was it stated that a customer can turn down a reefer sent to them if the message on the reefer conflicts with their business. An example would be if cheese company A gets a billboard reefer with cheese company B on it, company A can turn it down and the railroad has to replace it free to the customer, and within the customers contracted time. This became costly to the railroad to keep track of these billboard reefers and that helped to stop their use.
Somebody also wrote that beer company reefers, with their noticeable advertising, were frequently broken into so their security cost was high. Some beer companies stopped advertising.
I did some research on reefers that were operating in the late 40s for my layout. I was surprised to find rebuilt 36' reefers were still in use, especially with the meat companies like Swift, Wilson, and Armour. There were several reason these privately owned reefers were still in use (and not because of warehouse door width), and they had very colorful advertising on them. Right now I am looking for a rebuilt 36' meat reefer with a paint scheme used in the late 40s. MTH also did 36' reefers, so I need to check those out too.
I quote from the ruling!
"(E) On and after the effective date of this rule [August 1, 1934] advertisements of shippers or products are prohibited on newly constructed or repainted refrigerator cars.
(F) Effective January 1, 1937, no refrigerator cars bearing advertisements of any shipper, consignee, or product, will be accepted in interchange or handled locally on any railroad."
Now the effective date of ruling (F) was subsequently extended to 1938.
So clearly the ONLY thing one could do with these refers as of January 1, 1938 was to park them on private property.!
Now in the late 40's early 50's some legal eagles found a loophole. You could "say" Swift but still could NOT say Swift hams etc.
There is a great book "Billboard Refrigerator Car" by Hendrickson and Kaminski.
And if you paid attention to MTH's product release June 25.2021 you will notice they reference this 1934 date.