I'm not convinced yet that 'picaninny' could refer to an adult of any description. The quote re: "Gone With the Wind" - "her character was functionally a picaninny" - does not support the notion that 'picanniny' was a term applied to adults, outside the odd instance of this sort of academic manipulation - or maybe in some run-of-the-mill mockery, along the lines of calling someone a 'big baby'. And the teenagers having made it into the 'Pickaninny Series' is far from conclusive.

I'll keep my mind open on the matter though, if you can come with more ... (don't take any unnecessary risks, though!).