I was reading through the flavor text on Zeus, and I think I’ve found definitive evidence that Guichuan is 100% a different ship. Ocean’s Edge takes place in the aftermath of the fall of the Jade Rebellion (which probably took place “off screen” during Frozen North), hence why we see reprints of their ships dispersed among the Big Six. Zeus’ flavor text describes the battle through which Blackheart took command of the Baochuan. Given that this occurs after the events of Davy Jones’ Curse, Guichuan is out and about somewhere at the same time as this battle.
Not really relevant anymore, but might be worth including in the notes for Boachuan vs Guichuan vs Zeus as the final nail in the coffin.