In between other things, I've made a good start on the next stage (based on the notes here). I've coded a transform which does the following (so far):

• Expands each owner to include full ethnicity information inside the owner element.
• Expands each title to include a full property element inside it, as well as a list of expanded owners, and a list of preceding titles.

This is already a long way towards creating the sort of big flat file that will make it easy to trace transaction-chains back in time.