I'm making some modifications to an open source project licensed under the GPLv2 (which will of course be released under the GPLv2) but I'm unsure what to do with attribution notices adjacent to the GPL notice at the top of each file. Each file has:
Copyright (c) <YEAR> <ORGANIZATION> <GPL> Author: <NAME> <EMAIL>
at the top. Now, for the research I'm doing one of these source files largely implements the functionality I'm looking for (60%+) but still definitely requires non-trivial modifications to suit my needs. I'd like to use the existing source as a basis upon which to build my functionality, either via significantly refactoring the class to allow me to inherit from and implement my functionality that way (significant work, best long term solution) or by duplicating the file elsewhere in the source tree and making modifications directly in that file (easiest, quickest, least abstract), I'd say that choice is here nor there however (beyond the scope of this question).
In either of those cases how would I handle those attribution notices? I wouldn't want to deprive the previous author of his deserved credit but is it possible to delineate the new development from the old? Is it a materially different case when it comes to copying the file and leaving the original unmodified vs refactoring the original and adding two new files (one with the logic of the original, one with the logic of my new functionality)?