Further to the stories on the union numbers, George Lafferty of the Victoria University Industrial Relations Centre emailed me to say:
Just a bit more clarification on this. Collective bargaining coverage in fact increased over the past year (by around 7%). Both public and private sector coverage increased, although the public sector increase was significantly greater.
Obviously the previous reports on collective bargaining were even more confused than I thought. I'll post more information as it becomes available. But in the meantime, you will find a PDF file attached to this posting that is the most recent journal article on union numbers.