Okay, because I wanted to put off doing laundry, I popped in my copy of the DVD to listen to the timeline commentary made by the screen writers. I wrote down the main points to post here. The part regarding what happened to Bill, since it’s the subject of the OP, I’ve quoted word for word.
10 years before “present time.”—Jack shows up in Tortuga to recruit a crew. Bootstrap Bill is already with him—he was already good friends with Jack at this point. Jack has the compass, knows about the treasure and the curse. Doesn’t believe in the curse. Takes on Barbossa et al.
One day out, Barbossa convinces Jack to give up the bearings. Then he leads a mutiny against Jack, leaving him marooned on a deserted island. Bootstrap Bill, although he probably doesn’t actually participate in the mutiny, stays on board. Jack is okay with this because he’s just “doing what’s right for him.” He’s following the code.
Barbossa, his crew and Bill go to the Isle de Muerta, find the treasure, and proceed to go party and carouse. It’s only after quite a bit of the money has been spent that they realized they have been cursed. The Aztec writing on the outside of the chest tells them how to lift the curse, although apparently they didn’t read it all at this point.
In the meantime, Bill has been feeling guilty. He thinks they deserve to be cursed for what they have done to Jack, so he sends the coin to Will in England.
“Barbossa got really pissed off, strapped him to a cannon, and dropped him into, as ___ tells us, the crushing depths of Davy Jones’ Locker—Implying that perhaps while Bill cursed is still alive, he may be a very thin puddle on the ocean’s bottom. So that’s what happens to Bill.”
So the pirates are cursed, trying to return all the gold to the chest. Only later do they realize that they need the blood, too.
Move to 8 years before “present time.”—Will’s ship is destroyed by a gunpowder explosion, sending the boy into the ocean. The coin touches the water, calling the Black Pearl. But the pirate ship is scared off by the presence of the Dauntless, so doesn’t retrieve the coin. Elizabeth steals the coin from Will.
And we know the rest from there.
(I apologize for any spelling or grammatical mistakes–my husband’s bugging me to get off the computer so I don’t have time to double-check everything.)