Actually, you are spot on in my opinion only... the second year ZL900 service manuals state on the back Vin #s 2301- and #s 4701-
This tells me that Kaw made 7000 the first year. The ZL1000 I have no idea how many US models they produced but I believe the Aussie models got 1400 built in 1987, any Aussie models over the 1401 Vin # were built in 1988. That is only speculation though on my part!
If you disagree I love to debate!