Hello Tom, My Brew line is from Andreas in the north and through several generations in Liverpool. On a recent trip to the Island, I purchased a set of microfiche, and the information I gave you came from that. When I saw your posting, I looked up John BREW and Isabella CAIN and saw that they married in 1796, which would cover the birth of your John in about 1800.
Other John BREWs born at that time were:-
John BREW christened 8/9/1799 @ Braddon; parents James DOWNS and Martha BREW;
John BREW christened 15/9/1799 @ Maughold; parents Robert BREW and Cath CROW;
John BREW christened 29/9/1799 @ Douglas St. George; parents Philip BREW and Jane CROGHAN;
John BREW christened 10/11/1799 at Douglas St. George; parents John BREW and Isabella CAIN (This is the one I think);
John BREW christened 29/4/1800 @ Malew; parents William BREW and Jane TEESDALE; and
John BREW christened 14/9/1800 @ Lonan; parents James BREW and Cath COWIN.
These were all John BREWs born at the turn of the century, and I think we can rely on the microfiche information.
Good luck with your researches, Peter Brew St. Day Cornwall.