a derivative work must be different enough from the original to be regarded as a new work or must contain a substantial amount of new material. Making minor changes or additions of little substance to a preexisting work will not qualify the work as a new version for copyright purposes.
Edit: Outside the US, of course, the rules may vary.
You’re right—according to this PDF on copyright.gov, the requirement is that
Edit: Outside the US, of course, the rules may vary.