No, once milk has been processed, bottled, and sent to the supermarket, it is not reused by manufacturers.

Milk that has been processed and bottled is sent to the supermarket for consumers to purchase and enjoy. It is not reused by manufacturers.  

Here’s how it works: Fresh milk is taken from farms to the processor, usually within 24 hours of collection. The milk is then pasteurised (to ensure it’s safe to drink) and homogenised (to give it that smooth, creamy texture we all love). 
  
After milk undergoes these treatments, it is packaged in bottles or cartons that are sealed, stamped with the appropriate use-by date, packed into crates and stored in a cool room before being transported to supermarkets to be sold. Once it reaches the supermarket shelves, it’s ready for consumers to enjoy.  

If milk expires before it is sold, supermarkets may choose to dispose of it by using it as animal feed.