Does anyone know who started using this to mean a form of amateur MMA rules?

And why shows use the term "NSAC Amateur"?

As far as I am aware there is no such thing as a fixed amateur rule set from the NSAC.

There are the full unified rules sanctioned by the NSAC that everyone is familiar with. They also have their list of guidelines and regulations for events, including amateur, but I haven't seen a fixed rule set from them that is the same as what people here call "NSAC Amateur".

It looks like guys in the UK have taken a common US amateur rule set, one of many used over there, and dubbed it "NSAC". Is it like the term "semi-pro MMA", another daft quirk of UK MMA that doesn't really mean anything?

Maybe I'm wrong, I don't have as much to do with the current MMA scene as I used to. Does someone have a link to this rule set with the NSAC actually having anything to do with it? I couldn't find any.