Huh, that’s interesting & good to know. Seems that Most Favored Nation is very much still a thing today: https://en.wikipedia.org/wiki/Most_favoured_nation
Does it perhaps have an advantage for the Japanese, namely that the four powers will be less motivated to demand concessions because said concessions would also go to their rivals?
That’s a good question. I think the answer is “no” because each Western power had lots of rivals.
The Cold War was a different story. In the Cold War, there were (in theory) only two opposing sides. The USA would fund basically anyone who opposed the USSR (and vice versa).