How do I know the results of the mass catch up? It seems to have worked:
root@dur:~# root@dur:~# nl /var/log/mailman/fromusenet 1 Nov 19 09:40:02 2012 (3035) alpha: [2..8718] 2 Nov 19 09:40:02 2012 (3035) alpha caught up to article 8718 3 Nov 19 09:40:02 2012 (3035) alpha watermark: 8718 root@dur:~#
only I don't see any such articles actually in the list.
You have it backwards. Mass catchup means ignore all messages currently on the news server and start gatwaying to the list with the next news message to arrive.
If you wanted to gateway all the existing news server messages to the list, you should not have done a mass catchup and if everything was configured OK, the messages would have been gated to the list the first time cron/gate_news ran.