A quick check shows that there is no correlation between the old BB post number and the new, so unless Henri got a translation file when he converted the board there is not much chance of automatically redirecting to the correct page

I think all the old URLs should display a page which explains what has happened to the board, and offer links to the new main page or the search page.

The very low number of posts we are seeing is good evidence that people are not finding the new board.