What do pre-order statuses mean?

1.  Pre-order is not available for this product / variant regardless of the settings. Turn on the toggle to make pre-order available depending on configured conditions. 
   
   
2.  Product variants have different pre-order statuses. Pre-order availability depends on selected variant.
   
   
3.  Pre-order is not available because there are still several items in stock. The pre-order button is displayed only if the quantity of items in stock is less than or equal to zero.
   
   
4.  Pre-order is not available because of reaching the limits of purchased items for pre-ordering. (configure in the product / variant settings)
   
   
5.  Pre-order is no longer available because of schedule expiration. (configure in the product / variant settings)
   
   
6.  Pre-order will be available later on schedule. (configure in the product / variant settings)
   
   
7.  Pre-order should be available for this product / variant. Open the product page  and select the variant to check that. 
   
   

Why is the pre-order button not displayed?