The MSNZ regulation is so similar to the planning permit that I mentioned in my earlier post - but the position of the measuring site must be approved by a registered acoustic engineer. These guys really know their stuff and will give you a point that will satisfy any authority.
In most events any variation caused by wind direction, low cloud, smoke! etc can easily be verified by cross referencing with previous sound records and would not be a problem with the authority.
The one vehicle that caused me more concern prior to an event was the Gould GR55B with Nicholson NME V8 - came in at 93 db[A]