Councils don't often know the dates.
If it was recent purchase, the original build cost in 85 is out of contention.
There will depreciation in the 95 reno and the Assets. Our guys will let us know when they inspect if a date seems odd. Equally, they often spot renos that clients didn't know were there.
Do you happen to have any photos of the property? If so, email them to me and I'll get a QS to have a look at them.
Scott