Full_Description

   When the input files contain records with equal keys, those
   records may not maintain the same order that they appeared in
   the input file. Specifying the /STABLE qualifier arranges records
   with equal keys in the order of the input files on output. If you
   use this qualifier when sorting multiple input files, on output,
   records with equal keys in the first file precede those from the
   second file and so on.

   The /STABLE and /NODUPLICATES qualifiers are mutually exclusive.