I'm not sure exactly what data WW uses, but yes, I'm sure that it's some form of pattern or hinting information.  

Knowing which vertices make up some feature is part of the answer, but it still doesn't really tell you how to line them up if they are shaped differently.  For example, just to start, suppose one nose is 2 inches lower than the other?  So you also need to know some offset/center type information.  But what if one nose has wide nostrils and the other has slim ones?  Or one's nostrils go relatively more 'into' the head compared to the other ones that go relatively more 'up' into the nose? Or up-turned vs down-turned nose tip? Or is just 20% larger/smaller overall (messing up how things line up) ?

In general, noses are actually probably somewhat similar between meshes, but some other features will have more of these types of issues (ears in particular, but eyes and lips as well).

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