Just for info I have erased these partition and I can create new partition there! So allso I think these partition can be mounted for something, for example you can store there recovery ramdisk and an kernel for booting them with kexec! If you realy need more info please search in xperia go forum (sorry, I forgot where I posted them, maybe in general section?!) where I created a thread related to custom partitioning on xperia go (changed userdata, cache...etc size, merged 2 unused partitons, increased data, created custom one...blabla!).
found my post -> http://forum.xda-developers.com/show...2418241&page=8
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