When you set up PayPal you're asked to set a start date for when you would like to start importing transactions from. As you import, this date changes based on the date and time of the last import. If you would like to import transactions from the past you need to change this start date.
Changing the Start Date
To change the start date go to Overview > Click the Pen & Paper Icon next to the PayPal Settings. From here, change the Start Date to a date in the past followed by clicking Update, you will now be returned to the Overview page. To import your transactions, click the Import button.
The PayPal importer does not bring in duplicates. Any transactions that have previously been imported into Tally or the Staging Area will not be brought in again.