the Address form on the last page contains the number 'el 12:58'. Adding to the logic you have already used, probably December 58. Around that time imports ( Marvel and DC predominantly but we also had UK imported comics at the same time) spelt the end of the Australian comic industry. but as to the answer to your question (and I could be wrong) but I believe that the Roosevelt Government,( in office to deal with the depression), used the opportunity to introduce regulations on industry that were not in place before, again I may be wrong, but I understand these regulations have never been popular with US companies but many are still in place today. Yes, you are right, many other countries do not have similar regulations. Unfortunately.
Link to the book:
El Lobo The Man from Nowhere 19