The
information reaching the aircraft from a VOR is the radial from the station
(QDR) encoded in the phase difference between the signals (that's what the 9 is
saying in the A9W designator).
The RMI
takes this and simply drives the tail of the needle to that figure on the card
and therefore the needle pointer is over the QDM.
If the RMI
is slaving properly and showing the correct heading then the orientation will
be correct and the needle will also be pointing at the beacon so you can see
the relative bearing also.
However if
it has failed the card won't rotate.
So you've
kept radial information and lost relative bearing.
The NDB has no information on the signal (that’s what the 0 in the N0N
designator means) all the information is derived from the onboard equipment
which rotates the loop aerial together with the needle which is slaved to it until it gets the null in the cardioid.
So now you
can see that the needle will always point to the station whatever the
orientation of the card or the aircraft, so relative bearing information is
kept but radial information is lost.