Surely the gauge would indicate a high suction pressure if the filters are blocked. Are they not on the atmospheric side of the gyros to protect them for airborne debris and if they were blocked, instrument indication would severely lag actual changes to attitude.
I would think the gauge range indicates the range, within which, the pressure needs to be to give gyro speeds that are sufficient to indicate changes of attitude and rate of turn with specified rates.
I think that's the most I've ever said on this forum, hope it wasn't all wrong!