Parts of extension are written by the company employees, parts are modified pieces of another extension. The other extension is licensed under Apache 2.0. The company does not want to grant an Apache 2.0 license to the modifications.
This combination looks legal but it's unclear how to properly include the copyright notices and mentions of the Apache 2.0 license.
Another has every file starting with this wording:
Copyright 2019 Another Extension committers Licensed under the Apache License, Version 2.0 (the "License");
and it also contains a link to Apache 2.0 license text.
Clearly section 4c of Apache 2.0 license requires that all copyright notices are retained in the modified files. So it looks like the company should append its own notice:
Copyright 2019 Another Extension committers Copyright 2020 Cool Company. All rights reserved.
It's unclear what should be done with "licensed under the Apache License" wording. If it's kept in place then the recipients of the code may decide that the whole derivative work is licensed under Apache 2.0 which would be no good. If this wording is removed then it's unclear how to fulfill the requirement of section 4a (give any other recipients of the Work or Derivative Works a copy of this License).
What's the proper way to place copyright notices and mentions of Apache 2.0 license in this case?