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All reports say you need iOS 9 for wOS2 update to show up. What happens when YOU click on update running 8.4? If it says you are up to date or you get a splash then you will have the answer.
 
Have you tried installing the watch os2 using ios9 then downgrading the iphone back to ios 8.4.1 and repairing the watch to the iphone?
 
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