Marc Martin wrote
I have a YahooGroup that I'd like to move to Nabble -- it appears that I can package up the group's old messages into an .mbox and someone can populate the Nabble forum with those messages?
Yes.
Marc Martin wrote
However, prior to my group being on YahooGroups, it was on a LISTSERV, with a different list name. If I build a separate .mbox for those messages, can both .mboxes (from the LISTSERV and the YahooGroup) be used to populate the Nabble forum to make a complete archive?
Yes. If the archives overlap, messages with the same ID will be imported only once. So everything should work just fine.
You can send the mbox files and the forum link to my email
h u g o [at] n a b b l e [dot] c o m.