Turned in a bunch of completed DOFF assignments while in General R&D at Memory Alpha. One put me over the Tier 4 Diplomacy (Ambassador) requirement. Lt. Ferra's store dialog pops up. However, there are no requisitions available for a diplomacy DOFF. In fact, there are no entries at the bottom for the TIer 4 requisition amount at all (just 1-3) while the other categories have all four (I believe).