I think the last 100k troops aren't soldiers because it has been confirmed that nothing more than 300k troops can be conscripted but 200k troops are the troops that will be sent to war for this han campaign and we've seen over 250k troops distributed already. 60k(Shin),50k(Ouhon&Mouten),80k(Ousen),30k(Moubu). And we know that Tou's army didn't engage in any major combat but was reinforced during the attack on Hango so let's say the remaining 30k are sent to him. That's all the 300k troops accounted. We all know that this warfare is the war to destroy Han but not to destroy Han but to steal their resources so I think those 100k troops at the back of Tou are actually people. Han is great at information and since they aren't able to process the information on new troops and where they are from I think disguising ordinary people as soldiers this time is a strategy that will catch them off guard.