I wouldn't think there should be a lot of ambiguity about this particular specification on any encoder. It only takes 1(!) individual to do the test and you'll have your answer first hand.
It's simple. Just hook up all of the inputs (defined as keys as you are likely to use) to one side of the button and Ground to the other. Press it while in a utility like Ghost key and watch what happens. Be sure to push it a few times, but not too fast. That's a lot of data to jam down the port at once. You'll also want to see what's happening.
For a little extra fun, selectively disconnect a wire or two at a time to make sure that the encoder is behaving the way you expect it to. Sometimes problems get masked if all of a ports pins or a large chunk of a matrix are activated at once.
BTW, if anyone wants to try this with a KeyWiz, leave the P1 UP input disconnected. You can only do 31 keypresses at a time without activating the Shazaaam! feature. If it was necessary to have all 32 down at once, a special version could be supplied without this limitation.
The GP-Wiz USB encoders could do all 32, but Windows wouldn't know what to do with a joystick pushed in all 4 directions at the same time

. I have, however, designed a "stick-less" version where all 32 inputs could be active at once. But it only works on Windows 2000 and up.
RandyT