It seems that "6 book series" in the screenshot was a typo in the
title element (and ultimately the database from which the web page was generated): when you enter the first non-ad link from the screenshot into a browser, it now says "5 book series". The series is identified there as consisting of the following books:
- Fooled By Randomness: The Hidden Role of Chance in Life and in the Markets (2001),
- The Black Swan: The Impact of the Highly Improbable (Second Edition) (fist edition 2007, second edition 2010),
- Antifragile: Things That Gain from Disorder (2010; second edition 2016),
- The Bed of Procrustes: Philosophical and Practical Aphorisms (2012),
- Skin in the Game: Hidden Asymmetries in Daily Life (2018).
Penguin Random House has a page for the Incerto series also lists just these five titles and an Incerto five-book bundle from 2021.
Box sets published before 2018 obviously contain only the first four books, see for example Incerto: Fooled by Randomness, the Black Swan, the Bed of Procrustes, Antifragile on Amazon.co.uk, Incerto Box Set: Antifragile, The Black Swan, Fooled by Randomness, The Bed of Procrustes (2016) and Die wichtigsten Werke des großen Zufallsforschers erstmals gemeinsam im Schuber: Der Schwarze Schwan - Antifragilität - Narren des Zufalls - Kleines Handbuch für den Umgang mit Unwissen (German translation from 2018 that does not yet contain a translation of the fifth volume). The French edition Incerto: Le Hasard Sauvage / Le Cygne Noir Suivi de Force Et Fragilite / Le Lit de Procuste / Antifragile / Jouer Sa Peau from 2020 also contains just five books, not six.
Wikipedia also lists five books for the Incerto series. Below it is the heading Technical Incerto, which contains just one book published by a different publisher than the Incerto series:
- Statistical Consequences of Fat Tails: Real World Preasymptotics, Epistemology, and Applications, STEM Academic Press, 2020.
The Amazon.com page for this book says that this book is "the first volume of the Technical Incerto, weaves a narrative around published journal articles". This indicates that this series will be aimed at an academic audience, whereas the Incerto series published by Penguin Random House is aimed at the general public. The screenshot in the question does not list Statistical Consequences of Fat Tails as part of the Penguin Random House Incerto series.
title element in HTML is the element that contains the text that is displayed in a browser's title bar (in browsers that still have one), the tab in which the page is displayed (hover the mouse pointer over the tab to see the full title), the bookmark (if you bookmark the page in your browser) and typically also in search results.