Foucault discusses his use of sources in a number of places, and his comments are worth bearing in mind in this whole discussion of historical accuracy and sources:
This article discusses whether you have to cite your sources:
But don’t get confused by this romantic description of the philosophical work: if someone is recognized as a philosopher only by the new concepts that he has introduced into the philosophical discourse [D&G], and if new and original are nothing but an illusion [Barthes], then philosophy is not the art of creating concepts but rather the art of rebranding preexisting concepts. The philosopher doesn’t have much choice but to refurbish and rebrand old concepts and present them as original ones.
This is a tough situation: if you don’t quote you are accused of plagiarism and of the hubris of being original; if you quote (explicitly – by referring to philosophers; implicitly – by reusing known concepts) you’re accused of not being original, hence – not a philosopher. The game is, therefore, to quote all along your thesis until that point where you bring up your own rebranded (yet necessarily preexisting) concept – that which you present and pretend to be your own.
I think the author gets himself into difficulties here because he seems to promote deceptive scholarship (“The philosopher doesn’t have much choice but to refurbish and rebrand old concepts and present them as original ones”), but it does raise once again the theme of citations, “the footnotes” and historical accuracy that earlier posts here have been concerned with.