The primary reason for this page is that Wolfgang Steinicke's exhaustive study of William Herschel's published and unpublished papers has created a substantial number of cases in which the traditional dates of discovery (usually based on Herschel's published catalogs of 2500 nebulae and clusters) do not agree with Steinicke's research. In addition, there are a few cases in which Steinicke's currently published database also disagrees with the discovery dates for other objects (primarily those found by John Herschel and James Dunlop), and even some in which my own study of the historical literature (and/or of others working on this topic) have resulted in a change of the "traditional" discovery dates.
 The main content of this page will be a table of NGC/IC objects for which the traditional and actual dates of discovery by William Herschel differ; but there will also be a table of similar cases for other observers.
 This page was created on Jan 15, 2018, and although I consider it an important resource it is not the main objective of my current work, so it will probably take years for it to be more or less complete.