The GPL FAQ is fairly clear:
Is making and using multiple copies within one organization or company “distribution”?
No, in that case the organization is just making the copies for itself. As a consequence, a company or other organization can develop a modified version and install that version through its own facilities, without giving the staff permission ...
The Apache license allows a derived work to be published under a different license and "retaining copyright and license notices" does not mean that all copyright notices must be in chronological order next to each other.
Thus, you can write the header of the file like this:
* Copyright 2020 Cool company. All rights reserved.
* < Your ...
It may help to read this answer to get a bit more insight into the mental model you're likely using, and how it sometimes goes wrong. In any case, it is likely that once someone has a copyright interest in a work, they retain that interest in adaptations or derivatives of the work until their interest expires due to the passage of time. No amount of ...