When I first read The Dawn of Yangchen, I was pretty solidly convinced that "Unanimity" wasn't a codename. I thought that it was just a description of what the zongdus' plans were: Get all of the shangs to cooperate together unanimously.
I wasn't completely wedded to the theory, but my idea boiled down to that. Chaisee and Dooshim (and presumably the other zongdus) had negotiated a secret pact amongst themselves to declare independence for the shang cities as a fifth nation. With their complete control of all international trade they've got more wealth than anybody except the central national governments, and the book was very emphatic on the power that money has. After all, the Platinum Affair was what had started this entire crisis.
Working together the shangs may have even outmassed the fortunes of the various world leaders, provided they all committed. Hence, "Unanimity". If they played the four nations off against one another that may have been enough to carve out their own independent realm.
As the story progressed and Yangchen continued to find absolutely nothing -- no shipments of weapons or stockpiles of resources or vaults full of cash -- I leaned more heavily into the theory. Because if I was right it wasn't a single thing that she was looking for, it was an agreement.
I'd say I was about 70% certain that I had it pegged correctly.
Of course, once the three combustion benders started blowing up Bin-er my certainty took a bit of a hit, but up until then I felt pretty clever with myself for having figured it out.