Shortround6
Major General
it's very important know if this are IAS or TAS speed
It is no guarantee but usually such limitations were given in terms of IAS. This way the limitation would remain relatively constant regardless of altitude and air density.
An allied pilot, having been given this knowledge in a briefing (or passed to him by other pilots) could simply check his airspeed indicator to judge if the Zero was getting into the trouble area with it's ailerons.
True airspeed would require a bit of mental calculation (or lots of experience) to figure out for each altitude.
I could be wrong though