See if this helps explain the situation. If I understand your question correctly, the shift is for different devices “seeing” different currents for one event. i.e. if a fault is downstream from a generator distribution switchboard/switchgear, the individual breakers for each of the two generators would see each generator’s individual short circuit current. However, the common distribution bus would see the short circuit current of both generators.

The result is that when compared to each other, the generator breakers and the downstream breakers do not “appear” to operate as a TCC would indicate. Each generator would see their respective current and the distribution board would see both.

As an example, let’s say each generator produces 50 percent of the total short circuit current and the bus sees 100 percent. (from both generators) The generator overcurrent device would see 50 percent less current than the bus so the bus device could operate faster than its time current curve indicates relative to the generator device. Therefor the curve needs shifted to account for the devices seeing different currents. This is often referred to as “apparent coordination”

This is similar to what happens with the primary and secondary of a transformer. Each side of the transformer would have different currents and so do the primary and secondary device’s. As an example, a 480 v to 240 v transformer has a 2 to 1 ratio and the secondary current is twice as much as the primary current for events on the secondary. You can’t plot the primary and secondary devices as normal, one needs “shifted” by the ratio to view the “apparent” coordination.

I don’t know of any standard but this is a pretty common requirement for network (multiple sources/paths) in a coordinate study. And then we can talk about how this affects arc flash calculations….