the problem is that you do not know why it is flashing - if there is one plane within range it will flash, but then you cannot tell if it is just one plane or one plane and 50 GVs. You know roughly how mant planes are in the sector, but you have zero information about the number of GVs. This is why we need the GV darbar - not to locate them, but to tell the difference between 0 and 50 GVs, especially if there already is a plane in the sector and the base flash tell you nothing about the GVs.