Unfortunately, with the NSW BDM, the only way to get more than is available from the item listing (which you obviously have) is to pay for the certificate. I have some "spares" of certificates I bought to check, and found they were not relevant to my family search.
OK, it costs a tiny bit, but the result might be valuable and - worst case is that you end up with a certificate you don't need.
Hang on to it, you might be able to help someone with it later.
Cheers
John