It's mostly a parts bin bike. After all, the rear caliper technically *is* the same casting as used on other Hondas. It's just that the drilling and tapping is swapped around compared to everything else.
The rotor it uses is also technically different from any other Honda but it's really a slightly differently drilled version of the rear rotor off the 1989-1997 CB-1/CB400F.
Let's take a look at just how many parts on the 919 came out of a bin as opposed to being made specifically for it.
* An important point: in the context of manufacturing "slightly different" equates to "a completely different part".
-- Engine cases ('96 to '98 CBR900), transmission shafts, and possible clutch assembly. With the exception of first gear all other trans ratios are different. Crankshaft, rods, pistons, valves, and a lot of internal components are outwardly the same, but "slightly different" in alloy or fabrication process.* The cases are slightly different: the upper rear engine mount is a rubber bushed unit, not solid like the 919, and the forward engine mount is not used on the CBR. It is sufficiently similar despite the minor machining differences noted to apply the word "bin".
-- Ignition coils. At least probably.
-- Handlebar switches.
-- Front brake calipers and master cylinder? Maybe. Rotors are an unusual combination of later hub dimensions and earlier rotor diameter. Dimensionally they look the same as the F4i, but the number of spools mounting the rotor to the hub is 5, not 7.*
-- Wheels. At least they look like F4i wheels.
-- Rear brake master cylinder.
-- Electrical connectors.
-- Common electrical components such as relays, fuses, injectors, etc.
-- Handlebar? Maybe an early CB350 or somesuch, but how many would still be in a bin? Damned few.
-- Cush drive hub? Possible.
-- Turn signals.
That's about it. I can't find similar forks or swingarm. Of course the frame and bodywork are unique to the 919. While the frame may look similar to the 599, there are sufficient differences to warrant an appellation of unique.
Yup, it sounds like a 100% parts bin bike all right ... NOT!