How should I mark a source file (with GPLv2) as a derivative work from multiple files?

Question

In a sense this question is an extension to How should I mark a source file with GPLv2 as a derivative work?.

I would like to publish a project where it frequently occurs that files are drived works of multiple GPLv2-licensed original files.

• each original file carries a GPL preamble with a copyright notice
• some files carry additional/secondary copyright notices below that preamble, probably predating the original project's move to GPL
• the GPL preamble of each file states that the header and copyright notices must not be changed
• the copyright notices in the GPL preambles slightly vary in the year and occasionally in the holder
• in one file the copyright notice is even missing

So, I believe that the right way would be to proceed like answered in How should I mark a source file with GPLv2 as a derivative work?, but clearly state from which original files the file is derived and list each file's preamble, including the additional/secondary if present. Each such preamble entry would be "decorated" with the original filename to track where it comes from.

However, some files derive from 20 or more original files. So all the individual preambles would bulk significantly.

My questions:

• Is it acceptable to "compress" the list by stating the GPL preamble only once, with the combined years and copyright holders form all the files it is derived from?
• Is it acceptable to just list the various secondary copyright notices below that GPL preamble without indicating which comes from which original file?
• Is it acceptable to unify duplicates from that list (merging the specified years), as this means that it wouldn't be tracked any more which notice stems from which file?
• Is there some other (entirely different?) policy to handle such cases?

All questions assuming that the policy to combine the file preambles is explained at the top.

I believe that whatever the answer is, it is probably applicable to GPLv3 as well. However it would be good if an answer would drop a note on whether it also applies to GPLv3 if known.

Answer 1

The requirement to keep the copyright notices intact is to ensure that people cannot make an (implied) false claim of authorship by listing only themselves in the copyrights when actually they built upon the work of others.

The requirement to keep the license notices intact is to inform the downstream recipients of the rights they get with regards to the software they received.

The GPL licenses do not require you to prove the provenance (where you got it from) of the code you copied. Or at most on the project level (which project did you get it from).

Is it acceptable to "compress" the list by stating the GPL preamble only once, with the combined years and copyright holders form all the files it is derived from?

It is acceptable to group all the copyright lines together (without indicating where you copied each notice from).

It is also acceptable to merge all the GPL license preambles into one. If the various sources mention different versions of the GPL or some leave out the "or a later version" part, then it becomes more tricky because you may have an incompatible set of licenses.

If all preambles without the "or a later version" mention the same version, then you must mention that in your preamble, also without the "or a later version". If that is not the highest version number among all preambles, the licenses are incompatible.

Otherwise, you mention the highest version you found among the preambles.

Is it acceptable to just list the various secondary copyright notices below that GPL preamble without indicating which comes from which original file?

Yes, that is fully acceptable.

Is it acceptable to unify duplicates from that list (merging the specified years), as this means that it wouldn't be tracked any more which notice stems from which file?

Yes, it is fully acceptable to have only a single copy of each license in that list.

As stated above, the copyright lines also don't have to stay with the license text, but they can all be listed together. It is inadvisable to make changes to those copyright lines other than to move them.