Just wanted to add another data point to support the fact that the Gold desk does have access to additional D inventory for Gold members.

Case in point: I booked EK 212 (IAH-DXB) in Y, late May, Friday evening flight. No D inventory available. Even I inventory was zeroed out (per EF), but the seat map showed empty. The international call from the US to the Gold desk in Dubai was worth it: the agent was able to process the upgrade without any additional prompting from me. However, the miles had to come out of my account, not the account of another family member (who is Silver), in order to access the additional inventory.