Dear Greg,
The gauge / scale terminology seems to be even more confusing than you write.
In Germany;
"H0" = Half zero = 16mm, UK "00" Introduced as manufacturing methods improved. Took off after WW2 I understand.
Gauge 0 = 32mm model track gauge. Standard 1435mm gauge prototypes modelled at 1:45. (In the UK used for 2 foot gauge at scale???, some models are regaugable inbetween 45mm and 32mm. A friend of mine has India Himalayan engine and coaches produced this way.)
Gauge 1 = 45mm, associated with prototype standard gauge 1435mm modelled at 1:32 (UK 1:30,5 US 1:29)
Gauge "2m" = still model track gauge 45mm, but used for narrow gauge prototype "Meterspur" 1000mm at a modelling scale of 1:22,5. This is LGB narrow gauge prototype models. Also known as "Fn3" in the US. Also, sometimes other narrow gauges are aproximated, like 750mm etc. And lately, standard gauge 1435mm are modelled at some kind of approximate variable scale - often different regarding length and hight and width! :-D - this is PIKO and LGB standard gauge prototypes. Importantly, the "models" are intermixable in size and operations with the narrow gauge prototypes.
Gauge 2 = 64mm model track gauge, representing standard gauge 1435mm prototypes at 1:22,5 How on earth this model track also goes under the name "Gauge 3" in the UK is unkown to me. It's VERY CONFUSING ;-D ! It's better to use "Gauge 2,5" ", which avoids this confusion.
Also, what would "Gauge 2" be in the US and UK???!!!
Some people model prototype operations where standard gauge and narrow gauge intermixed, sometimes on the same trackbed. Then combinations of 45 & 32mm or 64 & 45mm track is used.
If Maerklin used "Gauge 3 & 4", it would be interesting to know what track gauges they used.
Hope this helps :-D
BTW Th ebasic problem is using the word "gauge" wich should only denote track width, to also include a modelling scale. Gauge and scale should be used separately.