Just over a week or so, I received an email from a Tim Hannagan, who'd come across the family tree. He isn't Brian and Suzanne's son, but a member of the family down a different line altogether - but still connected by my great great grandfather. John DeCourcy's list turned out to have his father and grandparents on it, so I was able to include them all on the family tree online.
And then Mark Hannagan (Terry's son) wrote to me today - I hadn't heard from him in a long time, possibly not since he was living in Dunedin with his family. He gave me some details about his children's birthdates and names, because he'd found the family tree online as well.
And then I happened to check the Connections part of the family tree online and found that Anne Rogers' niece has a family tree on Tribalpages as well, and she is doing the Joyce side of things. Furthermore, she's sent me three pictures that we don't have, which I'll upload in due course.