You could prepend a day (e.g. 01) to help ParseDate() disambiguate the input format:

print UnixDate( ParseDate(   'NOV-07'), '%Y-%m-%d' ), "\n";
print UnixDate( ParseDate('01-NOV-07'), '%Y-%m-%d' ), "\n";

__END__
2010-11-07
2007-11-01
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Also, why do you specify '%Y-%m-%d' as the output format when what you say you want is '%Y/%m'?