So if the measurement of the door is 5.3 inches from the edge of the hinge, it would be reasonable to guess that the slab is over 5 inches long. The left most piece looks to be against the edge of the hinge (or at least closer than the other two). If it isn't against it, it is no more than 0.1 inch away. The end of the slab is at around 5.2 inches on the scale. That means the slab is approximately 5.1 or 5.2 inches long.
I'm not sure if the Umnumzaan is also against the edge of the hinge, it doesn't look like it. It definitely does not come as close to the edge as the new slabs. The Umnumzaan looks to be at least 0.2 to 0.4 inches shorter.
Of course the two doors may not be the exact same size and all the crazy distortion from matching the photos may throw off the measurements a bit.
For reference CRK lists the Umnumzaan as having a 4.77 inch handle and a 3.675 inch blade.
I'm still guessing the blade will be longer than 3.75 inches and hoping for 4 inches.