VMS Help SORT, Specification File Qualifiers, /STABLE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Specifies that records with equal keys are directed to the
    output file in their input file order. The default condition
    is /NOSTABLE.

    Formats

      /STABLE

      /NOSTABLE

1 - Full Description

    By default, when records are sorted with identical keys, the
    order of those records in the output file may not be the same as
    they appeared in the input file. Specifying the /STABLE qualifier
    in a specification file arranges records with equal keys in the
    output file in the order of the input files as specified in the
    command line. If you use this qualifier when sorting multiple
    input files, on output, records with equal keys in the first file
    will precede those from the second file and so on.

2 - Example

  /STABLE

      This example of the /STABLE qualifier ensures that records with
      equal keys will have the same order in the input and output
      files.