RFC 977 notes in section 3.10.1 that articles presented "should
    include all required header lines." In fact, modern implementations
    only require From, Subject, and Newsgroups header lines and will
    supply the rest; further, many implementers believe that it is
    best for clients to generate as few headers as possible, since
    clients often do not format other headers correctly.

    This implementation behavior is consistent with both Bnews and Cnews
    which would supply missing headers for articles directly submitted
    to them.