we take for factual information legal documents such as death certs etc. but realistically they are not all as cracked up to be.I don't think there is any way they could know for sure. She is believed to have been dead by that time since that is probably when DV disposed of the body so it's likely the reason they picked that particular date.
It's probably the closest the coroner could get to the time of death as it is impossible to know the exact day. Imo
I have two close connections with incorrect death dates on official death certificate.
one in particular I asked LE why and was told even though we surmise the time of death the fact is that person is legally dead only when declared by appropriate authority.
so someone who dies alone often has sketchy death dates.
**this relates to non suspicious cases not coroner related situations for clarification. **