While I do not know the answer to the OP's question, I think whether row 12 is assignable at all depends on the particular aircraft. This goes to the post of California.
Based on personal experience, row 12 of A330, A340, 763 and 767 is available for pre-assignment. It is for the A319/A320/A321 series of aircrafts where row 12 is for assignment at the airport.