How can I determine what items are shown as 'new'?

The 'new' items are actually triggered by the 'Date Entered' field (at the bottom of the first product screen). The current date is entered automatically when the item is first added. Then the system uses the most recent dates to determine the 'new' items, and displays one page of items (based on the Layout Style and Item Rows entered in the 'Catalog Setup' area). The items stay in the 'new' area until a later date item is added or edited.

The date can be changed when the product is edited. So an administrator could modify that date while editing the product if desired. The items with the most recent 'Date Entered' will be displayed in the new items listing.

Another option is to create a category called "New Items" and assign items there, instead of using the system-created 'New' listing. That way it can be controlled, and more than one page of items can be displayed.