ORDER BY usage and the optimizer

Does Oracle know that a table is sorted by a specific column without using the ORDER BY in the table create?  In other words, lets say I create a new zipcode table from two other tables which are both ordered by zipcode.  If I don't put an explicit ORDER BY in the table create, it will still be ordered properly because the input tables were ordered.  But should I put an ORDER BY in anyway so the optimizer explicitly knows about the sorting?  Or is the optimizer smart enough to understand this?  Or does the optimizer figure this out when