Thanks free_mascot.
But
"In SQL Server 2012...
Is it true for SQL Server 2005?
And these statistics created by optimizer are some kind of "auto created" ( _WA_sys_ ) statistics?
If i try to run this query:
SELECT STATS_DATE(OBJECT_ID('my_table_name'),index_id)
it returns a "last update" for this index statistic that is older than my index rebuild date.
Am I missing something?