This just loops back around to the same question then.
What is a regiment?
The way I see it, a regiment is just simply a team. That rule you quoted earlier was just to prevent people from being on multiple teams.
The way I see it, IV is just one big team. If they put together a competitive line to do NWL, good for them. I have no qualms with it as long as none of those players are on other teams.
As for what you said earlier about "how easy it is to do". It's not that easy. Making a brigade like that is similar to merging, and they can be quite complicated.
However all this is my opinion, it is up to the mods to decide what a regiment is, and they quite clearly have decided IV fits their definition. There is no debate to be had, really.