The provisional report is made from the grossly visible findings. This is usually done quickly because it's easier to make this report immediately after the autopsy when the memory is fresh, and there are guidelines that say this report should come out in a couple of days.
The final report includes the microscopic findings. Preparing autopsy tissue for microscopy is very low priority for the lab, and looking at the slides is very low priority for the pathologist, especially for hospital (non-forensic) autopsies. The situation is further complicated if there is a neuropathology consult for brain findings. Most final autopsy reports come out within a year for hospital cases, but the reports can take even longer.
If the person died of, for example a heart attack, then the pathologist would often see the blocked coronaries grossly, and the final autopsy report will probably not contain much additional information.
If the person died of cancer, then the tumor would probably be seen grossly, and the final report will further classify cancer.
From your description, I'm not sure if your case is a coroner's case or not. You may want to clarify with the coroner whether he is still involved with the case as a forensic case or if he has decided that the case will be treated as a non-forensic hospital case.