They do have the total number dead over that time period. The issue is deciding how many of those deaths are related to the storm. If a death certificate lists “renal failure” as the cause of death, but the reason they died was because the dialysis center didn’t have electricity, it doesn’t show up the same way as if someone died from falling debris directly attributable to the hurricane. They’re estimating the increased deaths over non-hurricane years which are attributable to the hurricane, not the total number of deaths.
