This year, the statisticians went all the way back to 2001, with major revisions starting in 2005. In their announcement, they stated that their revisions began in 2004. The reasons for the changes, in their words were as follows:

Every year, the Commerce Department conducts the Annual Survey of Manufactures (ASM). These data are a survey, and not a Census. The Census covers years ending in -2 and -7, conducted every five years. The Survey fills in the missing years. A Census is a major undertaking, with an attempt to reach every member of the statistical Universe; in this case, every manufacturer. The Survey, on the other hand, uses a projectable sample and other data (such as employment data, statistical models developed from the Census, tax data, and other sources) to measure the size and trends of industries until the next Census comes around.

The data series for printing shipments that we use every month is from a smaller survey (called M3), and every year they update the M3 survey process with the latest data from the ASM. Since the 2006 ASM is now completed, that is why major revisions were made to that year and not 2007. Since 2007 is a Census year, we can expect larger revisions to 2007 shipments data because of the much greater detail afforded by the Census process.