Yoann & Vehlmann’s first published Spirou story (after their one-shot) was this eight-pager from 2008, Back to the Rédak. (“Rédak” is short for rédaction, the publishing offices of a magazine; as an English title I’ve gone with “Raider of the Lost Archive”.) It is, among other things, the story of how Spirou got back into his old uniform…
As iconic as the bellhop uniform is, Franquin (who never liked it) actually got rid of the jacket as early as 1967, and by the time of Morvan & Munuera the only thing left was a general tendency to wear red. When Yoann & Vehlmann took over the series, one of their assignments was to bring the uniform back. Dupuis = Spirou, and Spirou = red bellhop uniform!
This has been scanned from the German album Am anderen Ende Angst and from the Journal de Spirou #3653.
The Dupuis building is, as far as I can tell, invented by Yoann and completely imaginary. (The real building can be seen here.) It also appears in this Gaston page and in the unused Zorkons Alert! intro, as well as in more opulent form in Dans la griffes de la vipère (Spirou #53, “In the Clutches of the Viper”; pp. 45-46).
“Mr. Archive” (Monsieur Archives) is the pseudonym of Thierry Martens, former editor-in-chief of the Journal (1969-1977), a great collector, and for many years the main writer of historical articles about the magazine (or comics in general) for Dupuis. He died in 2011.
When Spirou can’t find an old issue of the magazine, he looks for a digest album (album du journal, recueil, reliure). These simply collect a bunch of magazine issues under one hardcover, and are a convenient way to collect the Journal. The one he gets is #98, which collects issues from 1965.
The Top of the Page gag by Yann & Conrad that Spirou looks at is this one, one salvo in an ongoing feud between the two pranksters and De Gieter (Papyrus). This particular gag apparently fell victim to censorship and didn’t run in the magazine.
The Trombone Illustré (“Illustrated Trombone”) was a supplement that came with the Journal for a short period of time in 1977. The brainchild of Yvan Delporte and André Franquin, it offered more anarchic, modern comedy for somewhat older readers. Though short-lived, it has become legendary. (Its history is touched on here.)
Spirou ami, partout, toujours! (“Spirou: friend wherever, forever!”) was the slogan of the Spirou fan club, Amis de Spirou (AdS, “Friends of Spirou”), and indirectly a rallying cry for the magazine.
The “War” between the Journal de Spirou and the Tintin magazine was a bit of (mostly) friendly competition between the two leading weekly Belgian comic magazines, but perhaps more between their readers: with fans of the more action/realistic comics of Tintin facing off against those who preferred the more comedy-centric Spirou. The rivalry has been the subject of a book, Le duel Tintin-Spirou by Hugues Dayez, and an exhibition, Tintin-Spirou: Match retour. Tintin magazine ceased publication in 1988.