Update: my wife and I have successfully obtained our TN/TD visas, both valid for 3 years.
The advice of a consulate staff whom I contacted by fax was to ignore the telephone operators (most of whom asked me to set up a TD appointment for my wife only) and set up a simultaneous appointment for TN and TD. That worked.
Unsane, thanks for supplying your pdf doc. I showed it to the person when handing in my forms, and it helped explain clearly why we were applying for the TN and the TD at the same time.
Hope my case helps other people in the future.
Great! Congrats...