There were quite a few episodes where it was someone's birthday, but they still played the normal theme music at the end. In fact, there is only one episode I can recall that ended with them singing Happy Birthday, and it was a Season 27 episode where Gabi was sick on her birthday.
And as for Season 25 episodes that were replaced with the calypso music, those would be 3175 and 3185. That's for the closing. 3184 had the harmonica opening replaced with the calypso music, but still had the harmonica closing. As for Season 26 episodes, I'm actually not sure there were any, because by Season 24, they were already using the animated credits.