I don't know if it got easier, but my scores improved tremendously. The first 3 tests I got 17 7 18, it was INTENSE, I didn't know what the heck I was doing half the time, and I rushed to not run out of time.
After buying 5 more tests I spent 1 week planning out a war strategy against every section. This WORKED. I took the timer off for all the previous tests I took, and took as much time as needed to get every question right - but more important, I devised personal strategy for every topic. After that, I worked on the timing. After doing lots of problems I finally saw my scores jumping up. I finished in time and fared better subsequently. From tests 6-10 I was getting 22's. On test 10 which I saved till the day before the test, I got a 23. And on the real thing I got a 24. So if you see your scores improving on CDP, thats a good sign. Just make sure you master your strategies. On the real thing I didn't break a sweat cause I knew I was prepared already, plus I knew it was going to be easier not harde (thats how the test prep companies work).