In reply to Gabe Farkas.

When I made my comment I hadn't noticed that the primary driver of the currency bump in 1999 was the printing of $20 bills. Upon closer examination of the raw data, I see that there were more 20's and 50's (and to a lesser extent 10's and 100's) printed in 1999 than were in 1998 and 2000. The other bills either remained the same or slightly increased (as part of the general increase in most denominations) from 1999 to 2000.