No resolution so far.
I called SkyMiles support and they confirmed (as expected) that DM status is not necessary to use a GUC. I asked for an extension on my 2 remaining GUCs and the agent on the phone said her supervisor would not allow it (even after I pressed a couple of times). The agent said I could call back closer to the GUC expiration date (Dec. 2015) and they may reconsider.
So I will call back in November and see what happens.
While on the call I asked them to confirm that there were seats in BE/D1 available and that there should have been space for GUC use. She said she called reservations support and they could not see that information, which I found strange.