count distinct from another workbook if between date range

[Rasscal]

as the title states im trying it count distinct values from a column in a table from another workbook if the values are between a certain date range(cell a1 & cell a2).

my current formula for the most part is

=SUM(--(FREQUENCY('FY18-FY19 PPD.xlsx'!$B$2:$B$51003,'FY18-FY19 PPD.xlsx'!$B$2:$B$51003)>0))

but how do i add if between date in cell a1 & b2?

thanks