No, I'm not clear what they are after either.
When you create a validation rule on a table field, Access asks whether you
want to check the existing records to see if they meet the rule. Perhaps
they are just asking you to answer No to that question.
Otherwise the request is ill-defined. You would perhaps need a field to
indicate the date when the record was added, and apply the rule only to
records that were entered after a certain date. It would be possible to use
the Validation Rule on the Table (in the properties box), not on a field, to
enforce such a rule.