They can't all be the same because the center blade has a different part number than the two outer blades. Note the different callout numbers in the exploded view. That and 16 x 3 = 48, so with 3 16" blades there is zero overlap, which means the deck would either not really be 48" cut, or just cut like crap with the wrong blades.
Center blade: IH-490476-R1
Outer blades: IH-490472-R1
What's keeping you from taking your own deck off and measuring the blades on it?