Recently, i found how to create holidays (like Easter) automatically using scripts (wiki.rainlendar.info/index.php?title=Scripts).

The page says it works on b75 or newer, but this doesn't take account of the new included/excluded option for calendars. So, only showed in calendars without included/excluded calendars selected.

These events have none calendar.
¿Could be a calendar called [none assigned] or something like that added for this events? I think, although, that setting a name for this "calendar" could be the same as an existing calendar...
but who will create a calendar called [none assigned] ?

I haven't really thought about that at all. I'll check if it's possible to add such special calendar for the include/exclude feature.