If certain products show No Stock Inventory Available on the product overview page, it means no default location has been assigned to those products.
To resolve this, you can either assign a location or book inventory:
Option 1: Assign a Location
Click Products then Overview.
Find the product you want to assign.
Click Actions then Manage Inventory.
Assign a location for the product.
Option 2: Book Inventory
You can also book inventory by following the Book Inventory In (Add Stock) article.
Please note that stock with No Stock Inventory available will not appear in some reports.