W2K CAL not timing out

I'm helping out with a W2k network with Exchange 5.5 that I am having trouble with. They have purchased 200 CALs for W2KS and Exchange 5.5 and all of the per seat settings appear to be correct - except for one thing, CALs issued a year and half ago and not used since then are not realeased to the pool. I can't find any MS KB article that addresses this.

Am I missing a seting somewhere? When I manually revoke the licenses, they are returned to the pool normally. I'm running out of ideas here.