The good news about the latest "new old" unreleased Rogue Trader figure in Bryan Ansell's collection is that we are able to positively ID it from its base tag: "Administratum":
Furthermore, we have an image of the Adeptus Administratum from the original Rogue Trader rulebook which clearly marks this figure:
The image is a pretty faithful rendering of the figure complete with book and dagger (or vice versa - I don't know which came first).
As per usual I don't know why this figure wasn't released. It's a fairly rough sculpt but I don't think it's too rough to have warranted a release. I would have bought one if I was in the market for an Administratum figure back in the day.
Neither does it seem to be a re-hash of another sculpt; the pose is not the same as any other figure I'm familiar with. If you are aware of a figure with a similar pose please let me know.
I'll leave you with a description of the Adeptus Administratum from the old Rogue Trader rulebook:
...And finally, there is still one more unreleased Rogue Trader era figure to come. Stay tuned!