Updating license and copyright in file headers

[Florian Moesch]

> But I don't think it is an exclusive list of the copyright holders for
> (portions of) the given file.
Why not? According to part 4 of the ISO Norm 16016, a copright mark in the form
of a "C" in a circle (or a "C" in parentheses), the name of the owner of the
right and the year of the first publication, declares that the designated owner
of the copyright reserves all rights to copy or use the published work unless
explicitely allowed otherwise.
The ISO norm 16016 may be a bit difficult to get access to, but you may also
want to read about international copyrights in the "Universal Copyright
Convention". You can e.g. read in the third article of that convention, that a
copyright mark should contain the year of the first(!) publication.
There seems to be no need to update a copyright mark when the protected work is
modified.
I still don't think it's a good idea to change a copyright notice someone might
have applied to his work in the intention to limit any use of the file to
exactly those rights that have explicitely been granted by the license
referenced in the file header.
Kind regards,
  Florian