Which is why it's so beautifully consistent.
A supernova should be predictable, years in advance. Hence an evacuation fleet.
OTOH, a supernova wouldn't be predictable down to the minute. Hence Spock launching on a mission and nevertheless being late. He must have launched before there was an explosion, because after an explosion, nothing would be unpredictable and Spock would not launch on a hopeless mission.
No distant star could meet all the criteria for Spock's mission. As of now, everything ever stated about it holds true in the same universe. Except perhaps for Spock's hyperbole of the kaboom threatening the galaxy. Although that, too, may pan out - loss of Romulus will not go without major interstellar consequence.
Now, did we hear anything about planets other than Romulus (and perhaps Remus?) being lost?
Timo Saloniemi