"Despite it’s ‘off the shelf’ style of design (indicating that the model was intended to be replicated at other parks) technically the Alton Mouse was the park’s first custom coaster since Vekoma never made another wild mouse, therefore making the coaster a unique addition to the park."
It can't be both off-the-shelf and custom, technically or otherwise. It was the only product Vekoma sold with that off-the-shelf design - but it wasn't at all custom. Far from it, it was actually manufactured as a demonstrator for the range.