/sys$common/syshlp/helplib.hlb INSTALL, ADD, Parameter  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 file-spec

    Names the file specification of an image to be installed as
    a known image. The file specification must name an existing
    executable or shareable image, which must have been linked with
    the /NOTRACEBACK qualifier. If you omit the device and directory
    specification, the default SYS$SYSTEM is used. The default file
    type is .EXE.

    The highest existing version of the file is used by default.
    However, you can specify another version of the file as the known
    version of the image. Even if other versions of the file exist,
    the version that you specify will be the version that satisfies
    all known file lookups for the image.