Reply to myself...
I can see now that there were proposed changes supposedly ratified in June last year that govern this, although the Unified Rules of MMA (New Jersey, not Nevada as I thought in the last post) website has nothing on new weight classes still. The UFC and other organisations opposed it and wikipedia lists the weight classes proposals as having been defeated, but other MMA/boxing news sites/forums have it there. Certainly, for the UFC it won't feature for them inside Nevada or any other state that decides not to implement, nor anywhere outside the States, so I guess that they will never implement these new weight classes. I guess California has adopted all the new changes with regards to weight classes, but then they ignored the changes to elbow strikes and instead banned them, and so that's why Strikeforce have this odd situation...
http://mmajunkie.com/news/4723/commission-updates-unified-mma-rules.mma This article from Junkie lists the same info, but doesn't mention anything about women's weight classes.
Still say that it's extremely confusing and counter-productive to have the women's weight classes using different names to the men's - especially when the same names are used, just for different classes.