The US government releases country studies,which are exactly what they sound like.
The 1990 one for Iraq estimates the Assyrian population to be 133,000 at the time.
This doesn't sound right.
I think the assyrian or generally the Iraqi diaspora increased starting from the 90s because that's when the first gulf war happened and Iraq was leading it's second war. Iraq was fairly stable during its first war i.e. Iranian-Iraqi war but, people knew this second war would not bring good news and they were right. Naturally, it would've declined so low in the 90s and even lower post 2003 to something like 100,000s.