Obviously, we detect objects by using the sensors we have. As you pointed out, those lifted off from the PRC at different times using different wind models to carry them. What we've seen is that those balloons and objects tend to follow wind patterns at altitude, and those change, based on the altitude itself.
For us, it became an element of interest when the radar picked up the high-altitude surveillance balloon as it started approaching the air defence identification zone. That's when we started attempting to characterize it and look at identification for that system.
A number of objects transit through the Pacific that we may not be tracking because they're outside of our sensors and because we don't consider them to be a threat to the airspace itself.