This needs a nested subquery that first consolidates data to unique records. That query then is source for outer query that counts records.
Assuming dates are always first of each month and data is multi-year, consider:
SELECT DateReceived, Count(*) AS Count FROM (
SELECT DISTINCT DateReceived, IDnum FROM Tracking)
GROUP BY DateReceived;
If dates are not always first of month and data is multi-year, consider:
SELECT YearMo, Count(*) AS Count FROM (
SELECT DISTINCT Format(DateReceived, "yyyymm") AS YearMo, IDnum FROM Tracking)
GROUP BY YearMo;
If data is not multi-year:
SELECT Month, Count(*) AS Count FROM (
SELECT DISTINCT Month(DateReceived) AS Month, IDnum FROM Tracking)
GROUP BY Month;
Strongly advise not to use spaces nor punctuation/special characters in naming convention, nor reserved words as names. If you do, must enclose in [ ].
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