>The Remarks section of the UPDATE STATISTICS (Transact-SQL) BOL 2008 topic list conditions under which Index/Column statistics may become inaccurate:
>
>- If there is significant change in the key values in the index, rerun UPDATE STATISTICS on that index.
>- If lots of data in an indexed column has been added, changed, or removed (that is, if the distribution of key values has changed), or the table has been truncated by using the TRUNCATE TABLE statement and then repopulated, use UPDATE STATISTICS.

Then, it would probably fall under the first condition.

Thanks