I think this version has been release at the same time, or just before, then their very first DVD-Rom version of the game for PC :
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At that time, Digital Leisure included 'hidden' additional game, unlock-able for a small fee. The DL DVD-Rom version I mentioned included all the files to play 'Space Ace', bit it has to be 'unlocked'.
They didn't included 'extra hidden game' anymore starting their famous 'Deluxe Pack'.