100 year old house

Hello, would appreciate any advice if possible

We are interested in buying a house built in 1900 in Sydney. Naturally because it is so old it does not have an occupation certificate

The current owners have done an extension and put in a pool which do have the appropriate council approvals/certificates

The property does have a studio in the back that the current owner says was there when they bought it and they do not have an occupation certificate for it (the studio also does seem quite old though so I’m guessing it was probably built prior to occupation certificates existing)

I’m a bit confused about the requirements of occupation certificates and BICs. Would these factors prevent you from buying the house if you were in my shoes? Is it necessary for old houses like this to have such certificates?