OK, I finally managed to get all the sounds loaded, and they appear to be in the folder that the Notion 4 sounds were in, but I'm still only getting the same few sounds that came pre-installed with Notion 4.
Edit - I thought it would be really clever to list all the Notion files on the computer in chronological order so that I could trace the missing sounds. Now I need someone to tell me something. The downloaded packages were right there in the 'downloads' folder, but there's no sign of what happened after I executed them, the packages are alone at the top of the list. On the other hand there are notion sound files that apparently pre-exist the packages littered all over the machine. The original Notion 4 folder has two full set of instruments in it even though I only had the default package, half of them are labelled 'Notion 4' and the other half carry no version ID, then there's a load more in the users/Deke folder which carry no version ID. Should there be a Notion 5 folder somewhere? The number 5 is rather conspicuous by it's absence in this list.
I also have both the Notion 4 and 5 icons displaying in the start menu. Should I just remove the icon, or remove 4 with the 'uninstall' option.