Well of course there is more than one genre listed for a lot of artists! Just because they have released one death metal song doesn't been that everything else they produce is going to belong to that genre. The most interesting artists tend to experiment with a number of different styles. The assignment of genres really has to be carried out on a song by song basis, and I agree, it's not easy!
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(list 6284, Mk1 S/N 00299 4GB blue [sold]. Mk2 S/N 080000094 20GB blue)