VMS Help CMS, DELETE, GENERATION, Qualifiers, /BEFORE[=generation-expression]  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Specifies the end of a range of generations that are to be
    deleted, excluding the specified generation. You cannot specify
    both /BEFORE and /TO or both /BEFORE and /GENERATION. You must
    specify the start of the range with either the /AFTER or /FROM
    qualifier.