Those Side Slip probes each report their measurements to their applicable ADR part of the ADIRU. The ADIRU provide the SSA to the respective PRIM. The data provided is used in all sorts of ways. Slip in turn, slip with E/O, crosswind slip, Y* law calculations and a great many other ways. If the SSA data to one ADIRU is corrupt then that data is excluded. If two ADR's receive corrupt SSA data then all SSA data is excluded and the flight control law reverts to Alternate Law.