My last attempt....
Each FCMC receives ZFW and ZFWCG from both FMGEC 1+2 - two independent values which should be the same.
Each FCMC compares the values it receives from FMGEC 1 with the values it received from FMGEC 2
If a FCMC detects a disagreement between the values it has been sent, it gives you an ECAM message.
IT HAS NOTHING TO DO WITH LIMITATIONS.......OR BS VALUES.
please excuse the shouting.....