>They prevent other companies from creating their own "generics" through a process called "evergreening" where they change patents in small, insignificant ways while still maintaining the patent on the core product.

To be really clear:

1) A company receives patent X in 2000, which expires in 2020.

2) In 2018, that company gets a new patent Y that is really patent X but with "small, insignificant" changes.

Are you saying that after step 2, that original patent for X is now extended or will that still go generic in 2020?