Why would you expect more than one neutral? It only carries unbalance current; the better the distribution planner/designer/engineer does, the less the current. Certainly two circuits worth of unbalance won't overload one conductor. Both circuits having a fault to ground on the same phase at the same time might be an issue, but the odds of that happening are diminishingly small.
Mudcat, youn are correct, 2 circuits of wye 3 ph 4 wire 24.9/14.4 kV sharing the same neutral. The same is true 12.47/7.2 kV. I looked up sections of G (Transformer connections) and H (Grounding)to verify their reasoning.
1) all poles are grd to the neutral. non device poles use a grd plate @bottom of the pole and device poles use a grd rod.
2) most 3ph xfmr banks primaries are delta. most wye 3ph banks prim. with a ungrd neutral and the rest use grd N.
3) 1 ph use the grd N and also surge arrestors, gang sw, both primary and secondary metering use grd N.
It is a little different but it will work. I would also believe the 2 - 3ph 4w circuits come of the same buss with separate oc devices ( bkr, reclosers ect.
Hope this helps and good luck
Dave
