Hi Berrie. Glad you found it of interest. If you can't find the births or deaths under either surname with variant spellings, it is possible they could be under another surname or not registered at all. For different time periods, the law was different. Going on memory, I think I read somewhere on stillbirths...you might find only the birth registered, or only the death, or both. Again, going on memory the law also varied over the decades as to how many weeks gestation was considered a stillborn (for example the stillbirth might occur at 34 weeks, but the law might have said 36 weeks or more was a legal birth, in which case no documentation was necessary as it would have been considered a 'miscarriage').
If something like this happened with your aunt, then maybe their might be hospital records or burial records only to discover.
The Royal Women's Hospital Paddington had an archive department which I contacted for my Nan's medical record from the 40s.
Hope you this helps you further. Katharine.