The Aiwa VCR probably outputs only composite video, which the OSSC doesn’t decode (it only extracts sync from it). Some VCR/DVD combos might be able to output RGB from VHS, but even there it’s a rather specific feature.
Pin 16 signals what the output device is sending, not the other way around.
A solution (though costly) is to add a Koryuu, but it, the OSSC and receiving device might not be happy with the rather unstable signal most VCRs output.
For capture, I think a dedicated composite video capture device is a better option.