ALFRED: ArchivaL Federal Reserve Economic Data

This project of the Federal Reserve Bank of St. Louis archives data from a given point in time (i.e. "vintage data"). As they put it: " In general, economic data for past observation periods are revised as more accurate estimates become available. As a result, previous vintages of data can be superceded and may no longer be available from various data sources."

http://research.stlouisfed.org/tips/alfred/