To answer some of your questions: Neil Hyslop's lettering first appeared in The Crab With The Golden Claws
which was first published in 1958. He continued to letter the books right up until one of the last books to be published in English, The Blue Lotus
, in 1983. The last colour book to be published was Tintin In The Congo
in 2005, but this contained a font which Moulinsart use in quite a lot of their recent books (I don't know actual the name of it). Most, if not all, of the books have been republished replacing the Hyslop lettering with this new font.
Let's also make a distinction here; Neil Hyslop's lettering is NOT a font. It's hand lettering and not a type face. People often think that it's a font because it's so neat and precise. Also, his lettering wasn't just limited to the text in the balloons. It also included any other writing that had to be translated, such as the "Booms", "Cracks", and other sound effects. All of these were meticulously copied and anglicised in HergÃ©'s style.
In the link you gave to previous mention of the Tintin font
take note of admin's post which links to Moulinsart's charter
**, particularly where it says "Copyright protects not only the comic albums and the drawings (...) but also the settings, the characters and their particularities, the names, titles and imaginary places, onomatopoeia, fonts
** = English-language version charter no longer exists; the French version can be found at http://www.tintin.com/home/legal/droits.html
(05 Jan 2015)