Well G scale isn't actually a norm, such as H0.

The scale of Norm II is 1:22.5 (22.5 times smaller than the Original) The Norm LGB used at the start (and still uses for Metergauge) is IIm (m for "meterspur" = metergauge/narrowgauge) which uses 45mm tracks The Norm II is used for full size Railways using 64mm tracks. But is rarely used because of the bigger Radius and there is no Major producer of Equipment. A single Freight Car can cost easyly 500€.

Today there is G scale which isn't a norm at all. Certain Gardenrailway enthusiasts say that G-Scale stands for "Gummi Scale" (Rubber Scale in English), because of the flexible scale from 1:29 to 1:20.5. But the common gauge is 45mm So you could Run a train with a "Standard" Gauge Locomotive and Metergauge waggons on the same Track.