L.Brown,
think you are right, the "Maitre" is not mandatory. Look at this find of 1874

http://www.lesgrosbarbares.info/lefaucheux/index.php?file=Sections&op=article&artid=164

Search for Defaure and you will find this:

"4° : Et Mr Jules Dufaure, avocat à la cour impériale de Paris, demeurant à Paris, rue Le Peletier n° 24."

He is only called "avocat" and not "Maitre"

Best regards,
Gunwolf