I have only read as far as your post, but doubt that original donor is O neg, because he couldn’t give it to Duncan, according to press reports.
Here's an interesting explanation:
Dr. Kent Brantly, the first American flown back to the U.S. for treatment of Ebola, confirmed that account, saying he spoke with a doctor caring for Duncan and was willing to donate blood. But their blood types were incompatible, he said Friday in an interview with Abilene Christian University’s alumni magazine.The above account on the failure to treat Duncan with convalescent plasma is alarming. The WHO has cited the use of convalescent blood or plasma to treat patients and posted a detailed 2014 report on its Ebola website entitled “Use of Convalescent Whole Blood or Plasma Collected from Patients Recovered from Ebola Virus Disease for Transfusion, as an Empirical Treatment during Outbreaks”. The report addresses ABO mismatches: When it is not possible to test the patient’s ABO group or if ABO matched CWB/CP is not available then: and recommends using whole blood if the donor is type O (universal donor) and to use plasma if the donor is type AB, A, or B (since plasma has had the blood cells removed).
Indeed, Kent Brantly was treated with convalescent antibodies from a recovered case (14M) in Liberia and he was the donor for three cases treated in Nebraska (Rick Sacra and Ashoka Mukpo) was well as the health care worker in Texas, Nina Pham. Media reports characterize one or more of these treatments as a plasma infusion, suggesting an ABO mismatch (which would preclude a whole blood transfusion, but not a plasma transfusion).
from here. I had thought he was type O- due to media reports, but the fact that he donated plasma makes that doubtful.