This is a rather good point.
Possibly, big nommie ship got asploded in the sun death-thingy it created, but even then there would more than likely be more than just one...
Hmm... and wonderment, if nommies were so active back 800 years before the FL single player, how come's they were supposedly 'awakened' by the Rhienland expedition finding an active artifact, if they were clearly awake enough to nuke Sol?
Interesting questions, and seeing as how Igiss is writing the new version of Sirius history for us (I mean, Cheese-eating surrender monkeys (The French) not running away from us wtf?!) how about he explain this hmm?
Anyone else got a theory, I'd love to hear them, much as Alkaleon here, I've always wondered but not cared enough to mention it...
EDIT: Aeternus Doleo ninja'd me so in response to you:
The SP was set 800 years after Sol went Kaboom, so between the sol-nukage and the artefact being found, why were the nomad's not in the same power in Sirius that they clearly showed when the raped Sol?