=IFERROR(INDEX(Sheet1!A$2:A$1000,AGGREGATE(15,6,(ROW(Sheet1!A$2:A$1000)-ROW(Sheet1!A$2)+1)/((ROW(Sheet1!A$2:A$1000)-ROW(Sheet1!A$2)+1)=MATCH(Sheet1!A$2:A$1000,Sheet1!A$2:A$1000,0)),ROWS(D$2:D2))),"")
If you create a list of unique items using Excel Online and the UNIQUE function, and later open the file in perpetual license Excel 2016, the values will remain until you try to update the formula (such as by changing a value in its data source). At that point, you should see a #NAME? error value