Count first entries (ignore duplicates) against multiple criteria

I have a table of data which has a column that contains a list of entries, some of which are legitimate duplicate entries (col A). In a second column I have the date that the row of data was entered (col B).

I would like to do a count of the first instance of entries in col A (ie count all unique entries and only count the first instance of entries which have duplicates) which are between certain date ranges in col B. All duplicate entries have the same value in col B

Can anyone out there help?

Many thanks in advance for your time.