/sys$common/syshlp/helplib.hlb CMS, DELETE, HISTORY, Qualifiers, /BEFORE=date-time  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Deletes all of the history information before a specified time. A
    single entry is made in the history file specifying that a section
    of the history data has been removed. This entry is made at the
    location in the history file where the lines were deleted.

    The time value can be an absolute, delta, or combination time
    value, or one of the following keywords: TODAY, TOMORROW, or
    YESTERDAY.  If the time value is a future value, CMS uses the
    current time.