CPE difficulty variations

Hello,

I have recently enlisted to take the CPE exam this June. As I was browsing online for more practice tests I stumbled upon a test which was significantly more difficult than the tests I had previously solved, tests found in some older practice books. The said books are the "CPE practice tests" books published by Cambridge between 2002 and 2005.
This particular test made me wonder (and worry) if the difficulty of the exam has varied over the years, if my books were outdated and if the tests they included were bellow the current difficulty level.
Could you please tell me if the difficulty level has maintained over the years or if the exams have grown in difficulty (or they simply vary from year to year) and I should urgently get some new more up-to-date books.

Thank you,
Dana R