Hi Chad Clauson,
I would introduce a "last refresh date" column in the data source. Then introduce a calculated field in Tableau that compares "last refresh date" with "TODAY()". If they match, no issues. If they don't match, then display the message.
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Since it updates everyday, you can create a field like this:
if max([date]) = today() then "Updated" else "Data Not Yet Updated" end
That will check if the max date in the dataset equals the current day.