Are you truly saying that the "confirmed" deaths represent the total of true deaths? There are no unreported or undocumented (by IBC standards) deaths?
That would be astounding.
Here in the modern, information highway USA, there are still people unaccounted for after Hurricane Katrina. These would not be confirmed deaths to the IBC. I am not knocking them or their methodology opr their purpose, but you do have to realize what their numbers represent.

They are not the true or actual number, they are an absolute indisputable minimum. The truth goes up from there. One can legitimately argue how high, and that is what the other studies are doing.