The first parameter to iterate functions does not have to be simply a table reference; it can actually be any DAX expression that returns a table. To demonstrate this, create the following measure:
Product = PRODUCTX(DISTINCT('R08_Table'[MonthNo]), [MonthNo]+0)
Place this measure in a Card visualization and note that the value displayed is 479M, or 479 million.
In this measure, we use the DISTINCT function to return only the unique values from the MonthNo column of our table, R08_Table. This returns the numbers 1-12. As our expression, we add 0 to the MonthNo column for each row in order to convert the expression to a numeric value from text. The PRODUCTX function then multiplies each of these unique values together. If you calculate the factorial of 12 (12!) on a calculator, the value is indeed 479,001,600, or roughly 479 million.