Schedule Orders job not updating the scheduled ship date when all product is in stock

We have a number of 'hold to complete' orders that have scheduled ship dates set out into the future.  When the product on the order comes in early to meet the demand from the order, sometimes the scheduled ship date is updated and other times it does not.  My understanding is that there is a job out there (Schedule Orders) that should perform this activity.  I am not familiar with the process so I am not sure how to determine why certain orders get updated and others don't.  These orders are all out there with the ship set in place