You should avoid using ddnames reserved for ICETOOL and DFSORT in ICETOOL operands (FROM, TO, LIST, DISCARD, WRITE). In general, you should also avoid supplying DD statements with ddnames reserved for DFSORT when using ICETOOL because doing so can cause unpredictable results. Specifically:

• SORTCNTL should not be used as a ddname in ICETOOL operators nor should it be supplied as a DD statement. A xxxxCNTL DD statement should only be supplied when you specify a USING(xxxx) operand. xxxx must be four characters that are valid in a ddname of the form xxxxCNTL. xxxx must not be SYSx.
• SYSIN, SORTCNTL, SORTIN, SORTOUT, SORTINnn, and xxxxINnn (where xxxx is specified in a USING operand) should not be used as ddnames in ICETOOL operators nor supplied as DD statements.
• TOOLMSG, DFSMSG, SSMSG, SYMNAMES, SYMNOUT, TOOLIN, SYSUDUMP, and SYSABEND should not be used as ddnames in ICETOOL operators.
• In general, xxxxWKdd ddnames should not be used as ddnames in ICETOOL operators nor supplied as DD statements. However, if you want to override dynamic allocation of work data sets for ICETOOL operators OCCUR and UNIQUE, you can use SORTWKdd DD statements for that purpose. If you want to override dynamic allocation of work data sets for ICETOOL operators DATASORT, RESIZE, SELECT, SORT, SPLICE, and SUBSET, you can use xxxxWKdd DD statements for that purpose in conjunction with the USING operand.
• DFSPARM (or the ddname specified for the PARMDDN installation option) should not be used as a ddname in ICETOOL operators. It should only be used as a DD statement to override DFSORT options for all operators, if appropriate. Refer to DFSPARM DD statement for details.
• xxxxOFdd (where xxxx is specified in a USING operand) is required as the ddname when an OUTFIL statement in the xxxxCNTL data set specifies FILES=dd. To avoid this requirement, use the FNAMES=ddname operand rather than the FILES=dd operand in OUTFIL statements, and include a DD statement for the specified ddname. See OUTFIL control statements for details of the FNAMES operand.

You should not use different DDs for a data set to be used for output and then input in the same step, if that data set can be extended to a second or subsequent volume, because that will result in incorrect output. See Data set notes and limitations for more information.