<p>I know the answer is probably obvious but... are there big enough differences between the different publishing years to merit paying $6 more for a more recently published (secondhand) one? And what's the oldest year that would be reasonable to use? </p>
<p>I know they're there to make the companies more money, but it can't hurt to make sure. ;)</p>
<p>The years are not very reliable. Most companies simply reprint it, correct a few errors and slap on a shiny new "2009" onto it. Why? Because it's lucrative to fool people to think that it's the "latest product" with "newer material" when it's the same. Therefore, I would not worry about the oldest year. You can purchase a secondhand one too if that doesn't hinder your ability to work on it.</p>