Hello Averil,
Alison's John Corkill died in Cornwall on 25th Sept 1828, aged 55 (Cornwall RO), so the Liverpool JC of the same age who died in the IOM must have been a different one. It was the Liverpool family who held the deed to property in the IOM, but when Frances asked Mark (your link) on this board whether the land was identified in the deed he didn't answer.
Alison's point all along has been that there were two families in England with fathers John Corkill who were both b IOM in the same year. Which wouldn't be surprising! Nor surprising that researchers who don't know about the number of Corkill families in the IOM at that time would assume they were the same person and merge the Liverpool and Cornwall families in their family trees. Then find all sorts of reasons as to why JC must be jumping between the two places and having wives and children in both.
Sue