The information provided by the informant on Vic BDM birth cert or a NSW BDM birth cert includes details about not just the baby whose birth is being registered, but the older babies born to that couple. It does not include implanted children raised by that couple.
In that sense, the birth certs are a far more reliable source of family history info for they include details about the baby's parents, the baby's older siblings, the baby's birthplace, the midwife/nurse/doctor/witnesses to the birth. On the other hand the death cert info has a section that includes family history .... so it includes info about either parent their spouse/s and children born within each marriage and is recognised by genealogists as far less reliable as the informant is really only sharing their own imperfect knowledge which, if a family member, is being given at a time of grief.
A baptism record has scant info and is less reliable than a Victoria or NSW bdm birth cert for 1850s and 1860s. It does not give details of when/where the baby's parents married, or where/when those parents were born or any details of the baby's older siblings.
It is important to remember that the rural deputy registrars, in NSW at least were meant to forward quarterly returns to their head office, but that there was no formal procedure checking up if the returns were not received. In the 1856-1860s timeframe in NSW, the Royal Mail coaches were often bailed up, it was not just gold that was taken, but the bills of exchange, land transactions etc. Quarterly returns for bdm were in with the Land Titles documents, afterall they were all destined for the same Registrar General. Likely a similar admin system existed in Victoria.
There have been probate cases that relied on proof of birth noted on the youngest childs birth cert as it listed all the older siblings of that child.
JM
Thanks Wivenhoe.
Im not sure that even seeing her siblings actual certs with her name on it would suffice because there is nothing stopping them just writing her down on the cert at the time and if she had been bought in as a baby and --- implanted --- into the family its still no proof we really need Hennriettas actual Birth or Baptism record