Isn't it alleged that some survivors from Crassus's army, captured by the Parthians at Carrhae and settled as 'military colonists' in central Asia, were suebsequently taken captive again in a Parthia-Han conflict and re-settled in China? There was a fair amount of distance between the Parthian and Chinese heartlands, even though their empires' borders were rather closer to each other...
There's a lot of supposition by people who want to see it happen, but in terms of hard facts it's all rather shaky.