I spoke to a guy at SNK-UK about the unreleased titles (At the time)
He said that only a few hundred of each title initially slipped out, and the rest were going to be sent back to Jp.
Thing is, a lot were bought post-pullout from the far-east and shipped back.
Which could explain why some are rarer than others, as everyone wanted Evolution, Cotton, Dynamite Sluggaer etc.
More mundane titles like Reversi and Picture Puzzle might not have been in such demand with the importers, so most of the stock may have been re-written.