Wasn't there a date somewhere on the newspaper that gets bled on that suggests it was set sometime in 1955?
That's really up to you to provide, and establish that it was intentional, and not simply an error, isn't it?
In the long run, I'd take the words of people involved in making it, over an un-confirmed point made by an unknown author on a web-site, wouldn't you? Looking at the page, there's another contributor listing many "errors" because they are adamant that the film is set in the "early 1930's" - a "fact" for which they offer no support, and at odds with the entry on the same page of the "fact" that it's 1955!
Therefore, it's both simpler and easier for me to think that the movie's art director is more likely to be right (and it's not the only reference in the book to period - for example, here's Keith Miller, Weta Digital Effects Supervisor on p. 98 "...there's always a unique challenge that's specific to each location you are working on, be it 1930's Manhattan, or 1940's Belgium.") than an IMDb contributor, especially when dealing with a film where *everything* has to be bespoke, made specifically for the production.
And on that
Your mention of the newspaper is an interesting idea, but leads us into another minefield. There's a running theme through the entire movie which plays specifically on the way that the books were presented in the international market.
While it's tempting to say that Tintin is Belgian, and he has indeed been turned into a Belgian cultural icon, almost an unofficial ambassador, Hergé took steps to reduce - rather than emphasise - the Belgian content over the years.
Early books make specific mentions of Brussels, and used landmarks in the capital to express the tie to that city; however he later decided to be more ambiguous, to increase the appeal of the series to other countries, and made efforts to make elements of older books more neutral when revising them for colour, and reducing mentions in later new books.
So he was happy for German readers to think that Haddock lived in Mühlenhof in German, Dutch readers Molensloot in Dutch, and British readers to have Marlinspike in English.
The film makers played into this amorphous locality by including multiple languages in signs, adverts, newspapers and what-have-you seen on screen - so Barnaby has a copy of Le Petit Vigtiéme
paper (French), which has stories in English, but a date of "Dinsdag" (Tuesday), which is Dutch or Flemish.
Further complication comes from the fact that, as far as I can see, the full date is "Dinsdag 12 Decem 1944" (presumably Tuesday, 12th December 1944, which is the correct day for that date). It's a blink and you'll miss it appearance, but that's what I got.
My guess is that it's been sourced from an old paper and just used for "texture", rather than to convey actual information, or is an Easter egg of some sort, with significance to the creator - so perhaps it's a family birthday or wedding anniversary (I checked if it was Steven Spielberg's birthday, but he's not quite that old, and it appears to be unrelated to the publication of the original stories on which the film is based, and wasn't a significant day (as far as I can tell) in the war in Europe at the time, although it is just before the Battle of the Bulge, so it might have a meaning I have missed, or perhaps relates to an event in something like Spielberg's Saving Private Ryan
, or Band of Brothers
But it's certainly before 1955! ;-)