The 12 treasures are the actual kiu sau faht, so they are applications for the bridges. There are no hard and fast rules, and different lineages will have different lists, but the key is understanding that they breathe life into the bridges. In many of the instances where the 12 bridges will denote a particular strategy and program for engagement, the 12 treasures will describe the quality of that engagement by giving you a particular method to use.
So, a simple one is Fun Kiu, or dividing bridge. You can use pek kiu, or chopping bridge, as an expression of Fun Kiu, but Pek will tell you what particular method of dividing you are using. It will also give you a clue as to what particular ging you are using. So this would be different from "snapping", or "tearing", but all of them would fall under the aegis of Fun Kiu.
Another example would be, when you are using a weapon and you use the method of "dim" (dotting or spotting), this is denoting the quality of Chyun Kiu, or inch bridge, that you are using.