"Lifespan" implies that at the end of the period, the old leaf died. There would be no other reason to use the word. The submitted article also mentions 45 hour

"Lifespan" implies that at the end of the period, the old leaf died. There would be no other reason to use the word. The submitted article also mentions 45 hours without a drop in activity, implying 100% at the end of 45 hours for the new leaf without any kind of assertion about a lifespan for the new leaf. The linked ACS release doesn't discuss this, either. Grant him the point. Truthfully, you're splitting hairs, and it really isn't worth arguing about, especially since this entire thing seems dubious without proof.