Well, stores know when they're going to have sales, but they don't anounce it before hand otherwise most people would just queue up to buy during that period, at a lower price.
All biz want money now, not later.
My understanding after reading that page is that each exam is a whole exam. Only if you need to have taken a prerequisite exam before taking a particular exam, and you have taken it, and THAT exam has expired, then you'd take an exam with only the updated information.
But then, why not take the exam with just the updated information as well?
Maybe I didn't get it.
--Carlisia