Well, if you're sure the game is there in full it's most likely a review copy of the game for a magazine or shop display.
Unfortunately, (p)review discs get sold on eBay et al all the time, usually for much less than the price of the retail game, so they aren't considered that collectable. This is because they are full review copies of the game, so there is nothing to gain from owning it (they often look more bland and have no proper case, manual or artwork).
While some better games like, for example, Shenmue II might fetch a bit more, you wouldn't get that much for it unless it was a prototype rather than a (p)review disc. Unless the game in question never goes on to be released. Good examples I can think of are... Rent-a-Hero No. 1 for the Xbox, Half-Life for the Dreamcast and Sonic Xtreme for the Saturn.
Still though, they are undoubtedly rarer than retail versions, and if one amassed a large collection of them I'd be pretty envious!