I kinda remembered something about that, but as P4 and S4 are now for all intents and purposes considered to be combined, I treat them as one. P4 is still way more demanding to model to for 'general' modellers, which is where an 'intermediate 18.83' could come in - I don't see it as much different in its way than modelling in general H0 is for most of the rest of the world - there's Proto 87 (?) which is finescale H0 as far as I can tell, but it's still the same basic gauge as normal H0.
I think I'll give 'Intermediate 18.83' a name: I83 :-) and it's got to be a CAPITAL I, so it's not caught up with all the iThis and iThat nonsense from Apple... ;-)
Ian J.