EGR valve: Am I being stiffed?

Hi, I have a 1999 Nissan Maxima with 69,000 miles on it. At the recommendation of my mechanic, I had the EGR valve replaced on my car in November 2005. I recently had some other routine work done (July 1 2006), and I had them diagnose what was going on with the car (the check engine light was on). They came back and said the EGR valve needed to be replaced. I became a little suspect since I had just had it replaced only 7 months earlier.

My question to you is, do you think it more likely that they just forgot to clear the diagnosis codes, or that the EGR valve needs to be replaced again? What should be an adequate lifetime for this part? Should this be the case, is it reasonable to request the work be re-done without (or with minimal) charge? For your reference, I later came home and researched how to check the diagnosis codes myself (the code read EGR Insufficient or Excessive flow detected).

Thanks for your help.