If I remember right, when there is no 'n' in the vector group designation, e.g. Dy11, the neutral is not brought out (not accessible for use). When there is an 'n' in the vector designation the neutral terminal 'n' or 'X0' is available.
The "n" stands for the neutral being brought out of the transformer tank and being available for current measurement or for being earthed. If "n" is absent from DYn11 that means it is an isolated neutral Delta-wye Xmer