How accurate are your sources?

The Columbia Journalism Review recently profiled the "Tilburg Checkers", a group of Dutch Journalism students whose fact-checking skills are being honed through an intensive course of re-fact checking mainstream press articles - an astonishing amount of which are incorrect in some way or another.

This article certainly applies to history as well. In researching my Master's thesis, I found mistakes which ran the gamut from:

CONFUSION - for example, Patricia Clavin and Jens-Wilhelm Wessels' ("Transnationalism and the League of Nations: Understanding the Work of its Economic and Financial Organisation." Contemporary European History 14, no. 4 (2005), 490) indictment of sloppy research on behalf of economic historians:

They often write of ‘Geneva-based ILO-LON economists’, although many of the League reports originated from committees comprising government representatives, such as the Delegation on Economic Depressions. League officials, League economists, members of the International Labour Organisation, League committees and delegations comprising national representatives are frequently, and confusingly, lumped together See Andres M. Endres and Grant A. Fleming, International Organisations and the Analysis of Economic Policy, 1919–1950 (Cambridge: Cambridge University Press, 2002).

To MISAPPROPRIATED ERRORS - such as assuming the title of a person, as seemingly presented in official sources, was indeed their title - without further checking.

In my professional experience i've even copyedited works who employed primary sources in their own way, mixing and re-ordering the quotation until it bore little resemblance to the original!

How frequently do you find mistakes in your sources? How do you address them in your research? Let us know!