Because nobody even answered the question!!!
Okay, maybe the question was too hard. Maybe I should have worded the question better. Maybe I created my next post too soon and nobody saw it. Whatever the reason, it was missed. Well here is the answer.
As I said in the post prior, there were 110 cards that made up this unique checklist featuring all 732 cards from 2004 Topps. However, it seems that Topps didn't notice but there were a few errors and some cards were missing. The question was how many cards and of whom?
There were two cards missing from the checklist and in both cases, it was because Topps put the image of the previous card in place of the real one. In the above example, Kyle Davies #313 card was missing, and Khalid Ballouli's card appeared twice.
The second card was the Edwin Jackson/Greg Miller Dodgers Prospects #689 card, which was conspiciously absent on the poster, leaving the Jeremy Guthrie/Grady Sizemore card, which, like the Ballouli card, to appear twice. Now in both cases, the full image of the card missing appeared on one card, not split into two, three, or sometimes four, different cards. So I actually took a scan of the missing cards, shrunk the image down to the size of the cards on the poster (as best as I could), and glued the images onto the checklist.
Is it wrong? Have I vandalized the cards? Is the sheet no longer in it's pure condition? Give me a break. It's my sheet, I can do what I want with it. Besides, who's going to notice right???