Library /sys$common/syshlp/dbg$help.hlb DEBUG, SET, TRACE, Qualifiers, /AFTER  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /AFTER:n

    Specifies that trace action not be taken until the nth time the
    designated tracepoint is encountered (n is a decimal integer).
    Thereafter, the tracepoint occurs every time it is encountered
    provided that conditions in the WHEN clause (if specified) are
    true. The SET TRACE/AFTER:1 command has the same effect as SET
    TRACE.