IIRC CLC (Centralised Load Control) will prepare a loading plan (LIRF) which the loading staff should follow. CLC will also prepare a provisional load sheet which the captain will sign. Once check-in has closed and all the cargo and bags are loaded the loading staff will send back the LIRF with the final layout of the containers in the cargo hold to CLC. CLC will then update the provisional load sheet for a final load sheet. It's at this time when it'll be found out whether the aircraft is out of trim, or balance. This could occur because the loading staff didn't follow the load plan provided by CLC, or that the anticipated number of bags or cargo didn't materialise or too many bags were checked in.