There's always the possibility that they produced more, unnumbered ones, to use as replacements for damaged, packed out SNed cards. There's also the possibility that these unnumbered extras found their way out of the warehouse without Topps managements' knowledge (i.e., not an official release) without replacing a damaged card. If I was in the market for one of these players (as I was when I found the Daulton), I would not even look at ones without the number on the reverse. (Just my opinion on that.)
As far as which serial numbers were destroyed, there are several examples on COMC with a SN in the 600s, 700s, 800s, and 900s, so it looks like after they sent the first 100 to the players, of the remaining 899, it's random as to which 400 were destroyed. There are also at least two examples of non-SNed ones, with no indication (Rick Aguilera - highest priced one, Todd Greene - lowest priced one). They do seem to exist, but not many and probably not from packs.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).