The Bluetooth boards hold a SOC which is programmed as an RS232 modem. The also comprise a legacy RS232 port.
The long side single row connector is used to program the Bluetooth SOC.
The header connector corresponds to the RS232 port. A flat cable can be crimped with a female header in one side and a female RS232 connector on the other.
An unmounted 4-pin single row connector provides a differential stereo audio output.