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

       /MATCH=size

    Specifies the number of records that should indicate matching
    data after a difference is found. By default, after the
    DIFFERENCES command finds unmatched records, it assumes that the
    files once again match after it finds three sequential records
    that match. Use the /MATCH qualifier to override the default
    match size of 3.

    You can increase the /MATCH qualifier value if you feel that
    the DIFFERENCES command is incorrectly matching sections of
    the master and revision input files after it has detected a
    difference.