The records of members transferring to the AIF show both a change of number and a change from a single letter prefix denoting the state of enlistment, ie, N, V, Q, S, W or T to a two (or three for PNG volunteers) letter prefix, eg, NX, VX, QX, SX, WX, TX, DX (ie Darwin) or NGX.  It was not a case of adding an “X” to the earlier number, which had no relationship with its replacement.

Service numbers with an X generally denote service with the Second AIF. However, if the number is 500,000 or higher, the person was enlisted in the Interim Forces.