I don't think the referendum was a particularly convincing one, but illegality under the law of the state being seceded from isn't a very convincing argument ei

I don't think the referendum was a particularly convincing one, but illegality under the law of the state being seceded from isn't a very convincing argument either. I mean, Ukraine's secession from the USSR was not legal under Soviet law. And Kosovo's wasn't legal under Serbian law. Consensual secession referenda, like the upcoming Scottish one, do happen on occasion, but are fairly unusual.