I should've done more research, it was late when I made the thread.IIRC they will be stored as titles waiting for update finalization, when their data is imported in title.db
All this in nand of course.
The system updates aren't stored in the NAND extdata. They're stored somewhere in the NAND in the NCSD format. I'll request the thread to be closed if nobody sees any use for it.
http://3dbrew.org/wiki/NCSD