I have, in the past had incomplete 14 x 12s but the last two years they have all been completely drawn with no real problem - just the one sheet of foundation that was left in, and not required, on one box - and that eventually went crooked and was scrapped. One does need strong colonies though, I think. Most of my foundation was drawn in the Dartingtons where the frames are away from the hive end walls and are warm way. I don't have any colonies on cold way with brood foundation to be drawn and that, I think, makes a difference, even with OMFs.
Re frame size: I have no experience of 16 x 10 but feel that a more square frame is better from the point of nest shape. Ideally the nest would be spherical for minimum surface area per unit volume (minimum heat loss), will go cylindrical because of over-head constraints (gaps between frames or Q/E) and needs a band of feed around the brood. The 14 x 12 emulates this satisfactorily for me, so I am contented with them.
Regards, RAB