Any other models in the official files that were not in the palette?
Yes. Quite a few. Especially in the toolset Beta, NWN proper and SoU. I seem to recall HotU .BIFs being much neater in that way and I'd imagine the number of unpaletted/unlisted items in 1.69 is fairly low in comparison. The extended beta for 1.69 had a lot of eyes looking over it before release but it's not unreasonable a few things slipped through.
Outside of 1.69 content, though, most of the stuff you're going to find floating around either requires work to bring to some level of usability or is only really useful to gain perspective on how something was done, or not done- like maybe the prototypes for the 3-part shields in the original NWN .BIFS or the .TXI command descriptions in the toolset Beta .BIFs.
Like any archeology, it's 1,000 pottery shards for every found earring.
If anyone's ever done something approaching a comprehensive survey of that crypto-content, I haven't seen it. But you will occasionally find mention on the old BioBoards or tucked away in a readme on the Vault that this-or-that was from some bit of recovered jetsam.
For instance, Google searches like this:
site:nwn.bioware.com "unused models"
site:nwvault.ign.com "unused models"