There are several registers being maintained by volunteers. See here -
viewtopic.php?t=40079Watto has been the driving force behind the Cooper S register, which is really an attempt to re-create the factory production records which were destroyed during the wind-up of the companies. There's a description by Watto near the end of the first page of this thread -
viewtopic.php?f=2&t=76418There's various opinions on how model registers should be managed. Some marques have a publicly accessible database. It appears some people don't wish to contribute because they value confidentiality of their car's information. Others don't want to contribute to a privately-managed database because they can't see the whole thing.
I'm one of a couple of administrators of the Cooper S and Clubman GT registers, or at least a version of them. I know several individuals keep their own 'registers'. Access is available on request, for example to see whether a car you are looking to purchase is recorded, to estimate the delivery date for your car, it's approximate engine number against others manufactured around the same time, etc.
I assume Watto is happy to receive comments or suggestions to improve the data and access to it.
Incidentally, no personal current or previous ownership information is divulged, unless it's significant, such as a works race or rally car, or Police service.