Good question. The remaining pins appear to be power rails along with three connections to the first 3 IO pins on port A of a 65C22 VIA.
VIA1 and VIA2 (65C22) schematic
So diagnostics connector perhaps.
Well done for digging that up! You clearly did much better than me with the research. Although I'm still a little lost ast to what it may be used for? Does this suggest that the logic board was somehow used in a different configuation a little like a blade? Or maybe this port was used during diagnostics in manufacture?
The unidentified J14 edge connector appears to carry differential serial lines.
Shown here on the Power Connector, Pullups & Pulldowns schematic:
and again on the Serial Interface and Sound Interface schematic:
Looks to go back to a 8530 serial communication controller and is shared with the external modem port.