Hi Brett,
I am not clear whether this is a question about when it is appropriate to have sub-forums or a technical one on how to manage (move/export/close) them.
The usual advice is that sub-forums are appropriate when you want a user to be able to use single logon (username/password) for a number of related forums. From a glance at the various sub-forums at:
http://maven.40175.n5.nabble.com/Maven-f40175.subapps.htmlthis would seem appropriate for many, if not all of them.
However, it is possible that there is an area of confusion, for you or your users, because as mail list archives many users will not wish to post to the lists via the forum (web interface). For them the need for registration at Nabble, to create a username/password, will be irrelevant.
In the past (and I note you are using "Old Nabble" and things may still work that way there) if you had split off a number of sub-forums from the Maven forum hierarchy then users that subscribed to a number of the Maven mail lists and who wished to post on several of the sub-forums, would have required separate usernames for each forum. However, these days usernames do not have to be unique across the whole of Nabble. It may be wise to ask the folks at Nabble to migrate your mail list archives to the new platform as it offers some benefits to users of the web interface to your list archives.
With regard to the "external" lists, again the issue is whether it will be a convenience to their users to have access to those archives through a common login at Nabble. It is possible that even though closed, that might still be useful to your users.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.