erexere wrote: I really got into looking at the May 1913 issue of National Geographic Magazine.
Erexere, this seems like a really worthwhile approach, although the Japanese clues did say something like "Look in a history book. What happened in May 1913?" Print magazines like National Geographic are normally laid out a few months in advance, though-- if you've still got access to those issues, it might be a good idea to page through the June, July and August editions as well.
Your idea also got me thinking: Surely, any major historical events would have been covered in real time by the major news outlets of that era, right? Well, it turns out that the New York Times has a searchable digital archive (link:
https://archive.nytimes.com/www.nytimes ... chive.html) of all their stories from 1851 on.
Since I'm personally biased towards an I1/V6 pairing for San Francisco, I ran a quick search for any articles about "China" published between 5/1/1913 and 5/31/1913. That month, it looked like the NYT ran an awful lot of stories about the USA's formal recognition of the Republic of China as a country.