I learned a most valuable lesson last night, and it's the reason the game mentioned in Parts I thru IV isn't showing as available. It goes something like this:

Once you buy it, it is no longer in the Playstation Store!

I feel humbled. To re-download something, go to your downloads page in the Playstation Store.  The Gripshift full-version has been available the whole time.

After that stupidity, I decided to get seriously pwned on Halo 2. Nice. I guess that's why my Xbox gamerzone is Recreation, not Pro!