Does corporate counsel knowledge have a half-life?

How true is it for in-house counsel that “50 to 70 percent of what they know today won’t be needed or cared about in two to five years.”? The quote comes from James R. Lucas, Fatal Illusions: Shredding a Dozen Unrealities That Can Keep Your Organization from Success (AMA 1997) at 91, and had within its targets all managers.

I visualize lawyers adding to their knowledge continuously, which forestalls decay (See my post of May 21, 2005 on spreading the learning from CLE.) At the same time, given the pace of change in laws, regulations, court decisions, and legal practice, if an in-house attorney fails to keep pace, that attorney’s knowledge is not the only thing to suffer a shorter life.