def get_referenced_filenames(license_matches):
    """
    Return a list of unique referenced filenames found in the rules of a list of
    ``license_matches``
    """
    unique_filenames = []
    for license_match in license_matches:
        for filename in license_match['matched_rule']['referenced_filenames']:
            if filename not in unique_filenames:
                unique_filenames.append(filename)

    return unique_filenames