Hey, I think that instead of making a new thread everytime you get a question you wanna ask, you should bring it up in General Chat. There're way too many threads floating around with only like 10 comments on them.
 
and plus, your question is something that could be summed up in one sentence:
Old-school isn't a genre. It just Means it's the beginning of something.
Atari 2600=Old school gaming.
Beatles=Old school rock n roll
Bathory=old school Black Metal

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InfinityZero, so how come bands that started playing even after 2000 can sound and play as oldschool as the precursors of the genre? I mean, 'oldschool' is more like a descritpion of a specific style. Nowadays when a band like Cannibal Corpse records an album, they have clarity, perfect mix and everything. Oldschool DM is more obscure, it has a 'garage' sound, it's simply raw. Even in 2011 there are bands that play 'oldschool' Death Metal, but they are mostly underground though. 

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Hails from Poland

As HACK has previously said on another forum titled "Best Old School Death Metal Band", there's a good modern day DM band called Kyrpts. Therefore it is possible for a modern day Death Metal band to make the listener time travel back the late 80's early 90's when brilliant albums were being produced. (Cause of Death, Warmaster, Into the Grave etc etc).

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"I Wish I had that AR-15 in here, then I could probably get out.....I don't like being locked up, it's not very nice."

-Martin Bryant, after the Port Arthur InfinityZero