Why FDI stock in the same year is different in the same reports? From World Investment Report 2003, in 2000, the US has 12.4% GDP as FDI inward stock and 13.2% GDP as FDI outward stock. These numbers are equivalent to 1274720 million USD, and 1356960 million USD. With GDP US in 2003 as 10.28 billion USD.

From World Investment Report 2007, in 2000, the shares above are 12.8 and 13.4, respectively.

From World Investment Report 2017, however, in 2000, the US has 2783235 million USD as FDI inward stocks, and 2694014 million USD as FDI outward stock. If we measure in percentage as above, we would have 27% and 26% equivalently. 

Why are the numbers are so different? Do I forget something like the price levels or so?

Many thanks for your help.
In note 1 of the World Investment Report 2017 (page 39), it is mentioned that 


  FDI data may differ from one WIR issue to another as data are
  continually revised, updated and corrected by the responsible
  authorities, such as central banks and statistical offices, that
  provide FDI data to UNCTAD.


The last figures are the most accurate ones.