I ended up using git log --grep=.... and have moved the packages. Using
'git blame' I found that a few copyright lines can be removed from
games.scm now. If a person has only imported a module ((gnu packages
base) for example), should I keep the copyright notice or lose it?

On Thu, 22 Feb 2018 11:43:51 +0100
Andreas Enge <andreas@enge.fr> wrote:

> On Thu, Feb 22, 2018 at 10:57:06AM +0100, Ricardo Wurmus wrote:
> > We need to move the copyright notices as well.  For that I usually
> > look at the git log for the packages that should be moved.  Since
> > we’re using predictable commit messages this can easily be grep’ed
> > from the git log.  
> 
> This would require to also look at all the other packages in the
> module, to decide whether the copyright notice should be moved or
> copied. Maybe "git blame MODULE.scm" could also be helpful in that
> respect: If used after the packages have been moved, it shows who has
> contributed to the remaining packages.
> 
> Andreas
>