Hi,
You can manually input sales prior to the 90 day range, just make sure you input all of the required fields so everything works properly.
The required fields that need to be filled in for manual entries are:
(Note: you can fill in as much additional information as is suited for the entry, but these need to be filled in at minimum)
"Item/Transaction ID (Unique)" - this can be filled in with any unique value
"Quantity" - self exlanatory
"Sale Date" - self explanatory
"Month Sold" - First day of the month of Sale date, can be populated by formula if you choose
"Sale Price" - self explanatory
I hope that helps, let me know if you have any other questions.
Scott