TEC59992 has been updated to add the following at the end of the document.
"Once you have reconciled all users have UID and GID defined, and have successfully cutover to z/OS 2.1,
you can then remove the DFTGROUP and DFTUSER assignments from the UNIXOPTS GSO record.
Note: z/OS 1.13 and below require the OMVS defaults be available for IOSAS processing."