I have three spare 5200 Prototypes:
Track and Field: -- SOLD! --
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Looney Toons Hotel:
Eproms with no stickers. No label on cart. Unreleased.
$175
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Space Dungeon:
No label on cart. This game was released but has a following for it's dual joystick action.
Eproms with one with a sticker 'Space Dungeon'
$75
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I haven't got a 5200 setup to test these, but I will guarantee that they function (as in start up) fine. None are dumped AFAIK, and they could be works in progress or finished versions.