Well I may have sort have answered my question here. All very tech stuff and way way beyond the limited bits of an exif I use.
I will post the two links as they may be of interest to anyone interested in editing the exif.
1) Link to Exif Tool by Phil Harvey
http://www.sno.phy.queensu.ca/~phil/exiftool/
2) 2) Link to the Exif Tool Tag Names to save scrolling through the above link.
http://www.sno.phy.queensu.ca/~phil/...mes/index.html
Kind of explains the fields in the exif that just contain numbers, by camera manufacturer. Not being a computer buff I found some interesting bits here that explain how a RAW processor ( in my case NX ) recognises things like the A/F point and various settings such as exposure comp, NR etc, that although adjustable, it initially applies when opening an image.
Don