The system has changed on new aircraft. Old aircraft still the same ie: FAC & FMGC independant.
The new system "FAC computes speeds based on FMS gross weights. Consistant PFD & FMGC speeds. In parallel, the FAC computes it's own GW & CofG, based on aerodynamic data which is used by ELAC & FMS for for GW cross check, and as a backup for speed computation in case of dual FMS failure".
If your aircraft has the new system, this will be the paragraph in the FAC FCOM section 1.22.40.p4.