The reason why Hergé provides no explanation for Haddock's Deus Ex Machina rescue of Tintin in Land of Black Gold (when Haddock tries to explain how he got there, he's always cut short) is that it's actually a meta joke. The original version of Land of Black Gold was initially serialized in a newspaper in 1939 and 1940, but after Germany occupied Belgium in 1940, Hergé thought that the comic would not pass the German censors because to its political nature, so the publication of Land of Black Gold was stopped mid-story. At this point Captain Haddock hadn't yet appeared in the series, so naturally he wasn't in the original Land of Black Gold either. Several other Tintin stories were published before Hergé decided to redraw Land of Black Gold in 1948, and in those intervening stories Haddock had become the most significant character in the series besides Tintin himself. Thus it would've been odd if Haddock had been left out of the new version of Land of Black Gold, but on the other hand he didn't really belong to a story that had been scripted before he even existed. This is the reason why Haddock is virtually absent from the story until the very end, and why there's no explanation for his sudden appearance. The lack of explanation is Hergé's comment on Haddock "invading" a story he wasn't originally a part of. So there is a solution to the riddle on a meta level, but not in the actual text.
Because Tintin in the Congo is often not printed that much anymore due to racism, Al Capone mentions a diamond operation in the Congo that is never mentioned again and makes the viewer wonder if s/he missed an adventure. This may seem like a Noodle Incident to the uninitiated.
Try watching the film and the American version of The Girl With The Dragon Tattoo back-to-back. Why is Blomkvist a pirate? Or alternately, being unsurprised at James Bond's swordfighting skills.
Thomson and Thompson were both less clumsy back when they fought zombies. They've defended the law before, even if one of them also played a pot dealer. For the other, you can see him in the cinema at the same time as a hacker; and they both lived at the Ice Age, but not together.
After Hergé announced at the end of Cigars of the Pharaoh that Tintin's next adventure was to be set in China, he was introduced to Zhang Chongren, a Chinese art student living in Belgium, who offered to consult on The Blue Lotus in order to avoid the stereotypes and caricatures typical of depictions of his homeland. Hergé accepted the offer, leading to a lifetime friendship. Zhang was even included in the story and known as Chang Chong-Chen. A humorous sequence has Tintin telling Chang about European stereotypes of China, which leads him to think that the Europeans are crazy.
Hergé was particularly meticulous in his research. He kept a huge collection of photographs, newspaper articles, and anything else possibly useful in future stories, and so many places and objects in the comic books are real places. For instance, the house of Prof. Calculus' Italian friend in The Calculus Affair is a real house that is still standing to this day. Furthermore, much of the scientific information in the books is accurate, or at least was accurate for the knowledge of the time, some apparent errors being a case of Science Marches On. In a odd case to Science Marching a 180 Degree Turn, one of Hergé's most well known "mistakes" was in depicting ice on the Moon (Explorers on the Moon), but since Indian astronomers have indeed found ice there, we probably owe him an apology.
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