There exist 2 versions of the legend you're right. Depending on the version, Excalibur and the Sword in the Stone were the same, in another, they are different swords.
If I recall correctly the movie Excalibur used the one where they are different. The Sword in the Stone was Uther Pendragon's that he buried in the rock just before dying from battle wounds. Arthur received Excalibur later from the Lady in the Lake as mentioned in other comments.
Admittedly I was young and deeply in love with all things Swords and Sorcery but I really liked that movie.
Ah well that's pretty much true of all old myths and stories. I know what you're saying but personally I think the variation we get on these stories in modern media is pretty incredible.
From the cheesy to the epic a lot of the books, movies, games etc. we enjoy today are just modern variations of ancient stories.
There's also a lot to be said for telling the same story—obviously the same story—with your own touch. Personal storytelling is a dying art—arguably already effectively dead. The most obvious version of this would be telling ghost stories, but who is even good at those anymore?
No, the in the movie Excalibur, Merlin recieves Excalibur from the Lady of the Lake, and he then gives it to Uther Pendragon, who on his death embeds it in the stone, leaving it for Arthur to draw it from the stone.
I like it, but it’s certainly not a normal movie by any means. It’s very much stylized – more like an opera or a music video than a normal motion picture, more epic mythic story than documentary-lets-pretend-this-really-happened. And I mean this storytelling-wise, not in terms of camera angles or colours or anything like that. Therefore, I suspect it’s not to everyone’s liking.
“I was not born to live a man’s life, but to be the stuff of future memory.” This quote by Arthur in the movie also applies, in a way, to the movie as a whole. The movie does not try to portray Arthur as a realistic medieval/fantasy king, but the idea of King Artur, the legend.
