Revisions reflect tax collection amounts obtained from three general sources. State and local government respondents have submitted revisions to amounts as originally reported. In other cases, governments have reported data, which we used to replace data that were previously imputed or estimated. Finally, some of the revisions were compiled from government sources, both published and unpublished. Current revisions are noted in each table by an "R" or, for Table 3, by a label next to the applicable figure, for appropriate quarters.