A. A lot, if they are significant.
The most closely eyed revisions in US data are of the unemployment and GDP figures. Unemployment figures are compiled on the fly and released within days of the end of the month covered by the data. The subsequent revisions can be substantial and consequential.
The compilation of US GDP is sort of a jigsaw puzzle. Different pieces of the puzzle are released throughout the quarter so the more the data is revised, the closer to reality (the government version) we get. The first release of GDP (advance GDP) is subject to major revision..
