The Grand total number of donors does not equal the sum of all the donors on the Comparisons and Summaries report
The Total Number of Donors does not necessarily add up to the number of donors from each field the report is run on. Donors can appear in multiple values but should only be counted once in the grand total of number of donors. An example is running the report on the ‘Gift Campaign’ field. An individual donor may have given gifts to multiple campaigns during the specific time period, however for grand number of Total Donors for the period, the donor is only counted one time.