I will support you for 10 years for this car I am selling you now.

(things change in-between for a year)

I will support you less than 5 years for this car, if you buy now.

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Google didn't do anything wrong legally, because the good sold a year ago is not the same as the good you are selling at current point.

YOu can have different support schedule.

Yes, it's very shady shit, because some people would find Chrome book in blogs/review a year ago thinking, oh 10 years, only to find out now it's less than that.