I don't think the first example can be held up, to be honest.
It certainly can't be proved, and you may well be right, Jock, that this is simply a deliberate instance of Haddock showing a bit of brain power and leadership; but personally, I was quite persuaded by IvanIvanovitch's theory that it's meant to be Tintin speaking. Whilst both of them do indeed have open mouths, Tintin's body language in that frame looks to me as if he's the one who's most likely to be speaking - particularly his extended index finger, which, combined with his frowning brow, is a gesture Tintin often makes when expounding a realisation or theory.
Given that Hergé drew the speech balloons directly into the panels, there would be little chance of the tail being reversed by accident
I agree that there's less chance of balloon tail mistakes in Tintin than in comics where the speech balloons are slapped on over the artwork afterwards. But penning the speech balloons may well have been a job delegated to assistants at this stage of Hergé's working life, so an error could have been made, which slipped past his notice when checking. And even if Hergé was penning his own speech balloons, it's not impossible to absent-mindedly draw a balloon tail going to the wrong character if working when tired, and stressed by the pressure of a deadline, which seems to have been the case for Hergé for much of the 1950s.
It would be interesting to see Hergé's pencil rough for the page, to see whether it's Tintin or Haddock who is given the speech balloon there. (Mind, it would be great to see the pencil roughs for the whole book, and indeed all the books, out of more general artistic interest and pleasure than for just checking this rather specific matter. But that's going off topic!)