The 100a rating is at 100% duty cycle. I have tested every model at multiples of the rated current. Heat buildup is the limiting factor.
It's a common port, so simultaneous charging and discharging would be averaged out in the external bus bars, and the BMS/battery would see the sum of the current in the system. For equal charge and discharge current, the battery would see zero amps.
Glad to know now that my assumption was good... given that my 8S unit just arrived.