A post in the main forum would have attracted Tibs attention and surely a more definitive answer
Yeah, that's very true. My point is that some "items" are not considered items for purposes of discarding when driven insane / knocked unconscious. For example, the Patrol Wagon and the deputy revolver do not count as "items". But the common items counterpart (sedanette, for example, and the derringer) do count, being common items.
Thus, the sedanette do count against the number of items allowed by a Back Injury, but the Patrol Wagon don't (and I guess your back is still aching regardless of what you're driving). The Dark Pharoah said that for purposes of drawing Exhibit items, you're allowed to every time you're instructed to draw a Unique Item. But that's the only thing they have in common. So, I'd play this literally.
As far as I remember, this was never clarified. But I'd love to know Tibs' opinion as well