A magnificent accomplishment for one person. He has scoured church and business directories, newspapers, details of politicians, WWI memorials. There must be 6000 or 7000 people covered. While he may occasionally go astray on inconsequential details (he's not always sure where Gallipoli is, and Church of Ireland deans are attached to a cathedral not a diocese), there is no reason to doubt the basic information. And it's also available online.