One must always be careful as to how the term "RSM" is used. In the majority of cases a RSM holds the rank of CWO, but not all CWOs hold the appointment of RSM.
There is also another title of "RSM" that all CF members, no matter their rank, even officers, aspire to; and that is "Retired Service Member".
So be careful how you go about using the term in conversation and correspondence.