Summary:

There are a few factors which allow us to confirm if a Product is Never-Diminishing:

You can check the Never-Diminishing toggle within the product record – if this is green, then the product is Never-Diminishing. If the toggle is greyed out, it is not a Never-Diminishing product. 

Never-Diminishing products also do not have the Inventory and Transaction tab that is available for standard products. Also, they do not display Stock On Hand, Allocated Quantity, information on the Details page.

Additional Information: 

• Never-Diminishing Products are not shown within shipments, as the system assumes no physical stock is being moved when these shipments are dispatched. 
• Why is the Inventory Tab Missing from my Product Record?