1, 2 or 1000 dates it doesn't matter. The SQL Statement generated by Crystal ensures the Date field is checked against each Range or Discrete value in the Parameter.

Because the parameter allows multiple Ranges and/or Discrete values a user could enter all of the following

01-Mar-1998 31-Mar-1998 'Range value
24-Jul-1997 'Discrete value.
17-Jul-1997 'Discrete value.
01-Jan-1998 31-Jan-1998 'Range valuie

The SQL statement generated by Crystal would be (depending on database and connection type)

InvoiceDate >= {d '1998-03-01'} AND InvoiceDate <= {ts '1998-03-31 23:59:59.000'} OR
InvoiceDate>= {d '1997-07-24'} AND InvoiceDate <= {ts '1997-07-24 23:59:59.000'} OR
InvoiceDate >= {d '1997-07-17'} AND InvoiceDate <= {ts '1997-07-17 23:59:59.000'} OR
InvoiceDate >= {d '1998-01-01'} AND InvoiceDate <= {ts '1998-01-31 23:59:59.000'}