It depends on what NS6 you have. Only the latest one should have an uninstaller file or folder. If all three have the uninstaller, it means that they were not properly removed. I, still, have a Netscape and a Netscape6 folder in the mail Netscape folder. The only one which has the full complement of files is Communicator, i.e.4.8. The other two folder have a chrome or components folder with very little little in them, and the plugins folder which has .dll files. This stuff is expected to be there, since it can be reused, especially the plugins.
I don't understand what you are saying about NS7.2. It will go wherever it say at the beginning of the installation. I am not sure about this, because I always make sure that I know where it fgoes, and, I select the folder, and rename it if necessary. The most important things is that you should have a folder in this path: application data/mozilla/profiles/default .
Earlier you said that you have a Users50 folder. Do you have also a Profiles folder. That's the one you want. In an earlier post, you said that you fished out of the recycle folder NS7.0, but that it did not have the Address book. It never had any address book. It should have been in the the Profile folder. Don't worry about anything which has only a few folders like I said, but you have to be concerned about any program which has the netscp.exe file. If more than one program has it, it means that it was improperly uninstalled. Nothing should be in the Recycle folder, unless you put it there. And, finally, only one program did not have an uninstaller. That was Netscape6.0. It was such a long time that I had it, that I am not 100% sure that I remember how to remove it.
But, you have many possibilities of having messed up, from what I gather.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax)