Originally Posted by Check Essential

Anything could happen if marketing changed their mind.

Not only backfills. They can cancel posted vacancies if they want to.
Right up to the time they publish the awards they can pretty much massage the numbers however they want.
They leave at least some "contingent vacancies" unfilled on almost every bid lately.

The only thing they can't do is create new vacancies without posting them. That would require a new AE.