Maybe Charlie was lying about not being able to swim....I don't remember the context in which he disclosed this.....or perhaps it was bad detail control on behalf of the writers. They've had a lot on their plate this season. I am surprised that they remember that Rose and Bernard are not a plant and a dog, respectively.
Charlie states "I don't swim" in episode 5 of season 1 which is titled, oddly enough, "White Rabbit." It is just about 1 minute into the episode if you have it.
I ahd a continuity thread but it'slong been buriedwouldadd this, TPTB make a lotofmistakes.
He did put it on his list, his brother could but when girl was drowning -season one- charlie did not go out to save her and when Des saw Claire drowning in season 3 - Des said Charlie would have drowned.