Effective June 14, 2001, data were reconstructed to reflect the switch from the Standard Industrial Classification (SIC) system to the North American Industry Classification System (NAICS).
Source: US. Bureau of the Census
US. Bureau of the Census, Total Business: Inventories to Sales Ratio [ISRATIO], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/ISRATIO, May 27, 2016.