Lintian is returning a false positive
unused-file-paragraph-in-dep5-copyright exactly when at the first
paragraph in the Files field debian/* is specified.
Without a concrete example, I can only guess that you did something
like this:
Files: debian/*
Copyright: 2015 Random Developer <randomdd@debian.org>
License: FooPL
Files: *
Copyright: 2015 Random Hacker <hacker@example.net>
License: BarPL
Here the following rule matters: "The last paragraph that matches a
particular file applies to it." And since the last paragraph matches
everything, the first one is unused.
The solution is to reorder the paragraphs: "More general paragraphs
should therefore be given first, followed by more specific overrides."