If the client expects to manipulate the data as a date in SPSS then input the variable using the appropriate SAS informat, likely one of the B8601 or E8601 depending on content, then export the data to SPSS. If worried include a text version as well. I would say it depends a lot on what you mean by "supports ISO 8601 format". SAS can read and write those formats but all of the internal manipulations are done with SAS date or datetime values.
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