From what I have understood, this is how the timeline was at the 3rd movie (Lot's of spoilers from the 1st, 2nd and 3rd movies):
Before the first movie, Hector Barbossa was recruited by Jack Sparrow as boatswain. Then he convinced Jack Sparrow to share the location of the Aztec Treasure. After that,
he abandoned Jack Sparrow on an island and went for the treasure with the rest of the crew.
Then, they all take at least one piece of gold and
William Turner Sr. sent one piece to his son, who was living in (England?).
And somehow, neither
Will Jr. nor his mother sold it.
1 or 2 years later Will Jr. decides to go to the Caribbean. He's the only survivor after the ship he was travelling was attacked by pirates.
From when the crew of the Black Pearl found the Aztec Treasure,
William Turner Sr. keeps complaining about having left Jack on that Island. After he sends the gold piece to his son, the crew gets tired of him and they tie a cannonball to his feet and they throw him overboard, where he meets Davy Jones and becomes a member of his cursed crew.
After that, the crew of the Black Pearl go on a crusade across the world looking for
the aztec gold pieces and taking any other gold they can reach, taking advantage of their cursed-immortal state.
Then we jump to the future to the plot of the first movie
where Barbossa dies.
In the third movie we see that
Hector Barbossa was one of the Lords of the Brethren Court (understandable given that he was immortal up until some years ago)
However, how was he able to claim one of the pieces of eight?
Unless he was an undercover Pirate Lord when he initially joined Jack's crew (difficult, since Jack would have recognised him), or he stole the piece from some other Pirate Lord while he was in his undead rampage, he couldn't be part of the Court.
Is that explained anywhere or is it a plot hole?