The "seniority" question is not straightforward either. The figure is arrived at from the time the squadron was "active", ie, front line and not disbanded. So for a start there are two "divisions", depending on whether or not the sqn was disbanded between WW1 and WW2. Those not so disbanded are likely to have the thick end of 20 years more "time in" than those who were .... which is one reason why 230 "beat" 72 for the NI sqn numberplate.
Once a sqn goes to reserve status, gets its (R) as an OCU or FTS, it gets no more seniority as it is no longer deemed "active", so will continue to lag even further behind ......