All regular G-Shock watches have unique model codes like GW-9400-1 or DW-5600E-1 or DW-6900SC-4.
But there are G-Shocks, which do not have their own model code. This often occurs with special editions or collaborations which are produced in smaller numbers only. Often they were not available from Casio itself but only from the partner of the collaboration.
In order to work properly, ShockBase needs each watch to have a unique model code. Therefore a made up model code is used for such G-Shocks. These models codes are anything but official and are only used for ShockBase.