I'm not sure about the consistency between manufacturing processes with respect to the edge coding (as opposed to notch codes), but I'm even more unclear about your objective of loading 3 sheets of 4x5 into a 5x12 holder. Are you thinking in terms of separating the image into three segments, individually framed? If so, I'm not sure I'd trust the film staying in position, and not overlapping as a result of being jostled during normal handling of the holder.