I'm a bit baffled. Were these certificates used as legal documents for identification of the vehicles? I always assumed your version of a vehicle title - 'vehicle registration document' - was issued by the government/county. Ours are registered by the State the vehicle is in.
I did note this on the '£6.00 for one question' - "Please note, this information is provided by email and will not be accepted by registration authorities. If you require a formal document you will need to purchase a Heritage Certificate."
Correus, if I am understanding your puzzlement correctly:
The legal document in the UK is the V5c, the official logbook which identifies the registered keeper (who is not necessarily the owner)
The Heritage certificate is provided by British Motor Heritage (a charity I believe?). It is an extract from the industry records but has no legal status as far as I know.
Others may contribute here, but I hope that helps.
Ian F