[Neil Jones]

IIRC the children's special for Series 3 (which was the first of that run, though Challenge treats those separately) still had the previous titles and font. As it featured games from Series 3, it must have been made after they took all the Series 2 games out.

So the decision to make the new titles and new font must have been a late call - I believe the Christmas Specials were the first aired for a series, with the main episodes following later (four months or so for Series 3). Of course post production can be done on any episode in any order so...