I'll have to take a look under mine tonight, but I don't see why they would need these spacers on the bookcase base to make it flush (mine doesn't have them), as they have that very nice leveling assembly...the one with the adjustment knob and the locking collar. Did some TAF's not have the bookcase leveling/adjuster assembly?
All that said, I do have these spacers elsewhere on my TAF....they are under a different mech. (I can't remember which one right now, but I did see them when I shopped it out). Perhaps someone moved them at some point, or maybe they were used as needed on various things.