Well I found the data the kind folks at NCH had placed Express Invoice files in the Shared Folder, I can't recall having made a Sharing Decision on install
Key Principle= Secure by Default, not Share by Default!!
Again, can't complain too much as for this part of the software it is free. However it leaves me less likely to upgrade if the security stance is not right on the Free part of the software.
So to recap
HD/Users/Shared/Library/Application Support/NCH Software
Moving to another platform appears to trigger a re-install so I suspect there is a Prefs file I haven't tracked down.