The sub cells are NOT BALANCED / NOT MONITORED, right?
They are not monitored, no.
If you look at the multi-pin connectors on the edge of the PCBs they look to be carrying 16-18 connections each, therefore no more than 36 'data' lines to the monitoring system.
Also if you look at the actual connections to each cell, the only connections are to +ve, -ve and the shunts between cells.