He is talking here about his artistic estate, rather than documentation (normally referred to as the written estate, when dealing with an artist's Nachlass).

Core oeuvre:
in the end one has to deal with the
contradiction that Boltraffio on the one hand got harshly dismissed, and on the other hand,
and very likely, still included into the the core oeuvre, while it remains unknown to what
degree;
http://authenticationinart.org/pdf/papers/the-unique-propert...

http://www.artbook.com/9783775738514.html

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Note added at 21 mins (2018-07-26 18:32:38 GMT)
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Core body of work:

To a certain degree, the perception of delay is the product of the way that
Duchamp's career has been framed. In the standard summary, we find the paradox
of the amazing importance of an artist whose core body of work (with the exception
of certain scattered items and his secret last work) was all produced in little
more than a decade, in the period of 1912 to 1923.
https://archivariusblog.files.wordpress.com/2016/01/70-autum...

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Note added at 22 mins (2018-07-26 18:33:34 GMT)
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The Verzeichnis mentioned may be a catalogue raisonné (Werkverzeichnis), rather than merely a list.