This has been bugging me for a while. When I select a column of data (with duplicates) and remove duplicates, it says '421 duplicate values foundd and removed; 481 unique values remain'. Great. A count of the column shows that there are indeed 481 values left. But then if I do remove duplicates again, on the same column, I get the message '420 duplicate values found and removed; 842 unique values remain'. A count of the column shows that there are still 841 values, so I think nothing has changed (as would be expected), but why do I get a different message from the remove duplicates tool?