I have to say that I would really put a lot more store in what you see now, than in one subtest score from a test that your DS took 5 years ago. That's a long time ago, and there are many reasons why a five-year-old might have scored lower on a particular subtest.
If you don't see anything now that gives you cause to worry, then don't. And keep in mind that how your son functions in the real world--in school and activities and at home--is far more important than whether he can arrange blocks into a given pattern within the specified time limit. Yes, testing can be useful, but it's very limited in what it can tell you.
On the other hand, if there is a reason to test--some particular concern, or you need the scores to qualify for some services, schools or programs--then test.
