No, they do not come out to 12-1/2" unless you did some crazy measurements. If you were to start your 9 patch with 5" charm squares, your finished block is 13-1/2".
You could trim it back to 12-1/2, but not sure what that would do to the design. You could try one with scraps and see what you think. It only takes me 15 minutes to sew, cut, rearrange, sew it back together.