VMS Help LBR Routines, LBR$SET_MODULE, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    If you specify bufdesc, the LBR routine returns the module header
    into the buffer. If you specify buflen, the routine also returns
    the buffer's length. If you specify updatedesc, the routine
    updates the header information.

    You define the maximum length of the update information (by
    specifying a value for CRE$L_UHDMAX) when you create the library.
    The Librarian zero-fills the information if it is less than the
    maximum length or truncates it if it exceeds the maximum length.