Record data immediately at the time of the activity. Never backdate entries or use "scratch paper" for later transcription.
It is possible you meant GDP deflator code 439 (used in some legacy ERP systems to adjust nominal GDP to real prices). Check your original source document for a missing colon or space. gdp e439
: The book explores why GDP was better at measuring 1940s-style "physical mass production" but struggles with today's intangible assets. In 1947, about half of the economy was easily measurable; by 2019, that dropped to less than a fifth. Record data immediately at the time of the activity