The DATA step has the potential to destroy the sorted order.  For example, this would be a legal program: data new;    set already_sorted;    by id;    if amount > 1000 then id='ABC'; run; The new data set is not sorted, even though the incoming data set is sorted. If you know that the sorted order is going to be maintained, you can add that as a data set option: data interleaved (sortedby=id);    set a b;    by id; run; If you then run a PROC CONTENTS, the sort indicator will be maintained.  However, the second related indicator (VALIDATED) will not be set because SAS has not validated the sorted order. Finally, when you use the SORTEDBY data set option, you better be correct.  If you are wrong, the data will not be in order but subsequent PROC SORTs will be skipped.  There are ways around that, but it's better not to get into that situation in the first place. Good luck. ... View more