My best guess is that it could, probably even higher, but that the documentation did not survive. My bet is that the 167mph flap setting is the first stage of the landing setting.
The Ki-84 was built to higher strength factors than any other Japanese aircraft. I find the idea that they would have put combat flaps on it that could not be used above 167mph to be absurd.
The Japanese were even more thorough than the Germans were about destroying documents.
That's not really true, though. Maybe on paper in the earliest stages it was designed to be stronger, but in actual implementation it was nearly a disaster. The best and most reliable and strongest versions were the FIRST off the production lines. As the war continued (and remember, this was already a late-war plane) the quality dropped sharply. Failing landing gear because the metal was so poor that the struts snapped, engines that were bombed out of existence and derated replacement engines that were so poor they often performed a fraction of how they should have, and most pilots had to wonder if they would even get to altitude with the rest of their wing when they scrambled for a sortie. Metal quality, slave-labor-conditions, constant bombing of the production facilities, all resulted in the mid-production-run Ki-84s being bad quality and the end-production ones being worse.
Keep in mind the Ki-100 was no better than the Ki-61 in terms of raw performance but it was far far better than the 1945-era Ki-84s rolling off the lines. It was actually faster, climbed better, and ultimately more reliable to get the pilot TO and FROM the combat than the Ki-84s available at the time.
In AH we have a version with almost no production faults -- an early model, if you will (one of the best). However, in reality the documentation may state the speeds it has because the very metal of the flap surface wasn't capable of sustaining faster speeds, or the lever-actions for the flap deployment or the tracks on which they slide may be so unreliable that putting them out any higher would risk major damage to the airframe.
Maybe on a pristine model, it might have higher speeds, maybe not. I don't think "lack of documentation" is the reason and I think you shouldn't assume the Ki-84 was a stronger or more reliable plane than others at the time. If it were, you'd never have seen Ki-43-IIIs ever get the green light, nor Ki-100s ever take to the skies. They were filling the role that the Ki-84s left wide open.
