Simon,
You are not allowed to call your event "International," either, unless you are an ISAF Class.

You also are not allowed to hold a regional event, like a North Americans unless you are an ISAF Class, AND unless the "Region" is officially recognized as such by ISAF. In the case of North America, we would have to form a North American Sailing Association and get it approved by ISAF in order to "legally" hold North American Championships even for ISAF Classes.

Another example is that there was recently a Caribbean Championship, but that was not ISAF-legal. Supposedly, the Caribbean nations are trying to organize and get ISAF approval as a region, so they can legally hold Caribbean Championships.

All of the above is based upon what I was told by Paul Henderson when he was ISAF President. I suppose this does not necessarily mean that all other ISAF officials interpret the regulations the same way.