Why did all of my motor oil consume after a year of having it changed, with no hints? No smoke nor leak?

I changed my motor oil in my 2006 G35 Infiniti Coupe about a year ago and just realized that all the oil had been consumed without a trace of smoke while driving or leak from the vehicle. I just had it filled again with a synthetic oil. What could have caused this? I am even suspecting a mechanic (a different... show more I changed my motor oil in my 2006 G35 Infiniti Coupe about a year ago and just realized that all the oil had been consumed without a trace of smoke while driving or leak from the vehicle. I just had it filled again with a synthetic oil. What could have caused this? I am even suspecting a mechanic (a different one from above) of having dishonestly drained it recently so that I would have to go back to him for filling oil.
Update: In other words, after a year of having oil changed, my oil was all dried up. GONE. With no smoke while driving, and no traces of a leak. Had it mainly parked in my garage and hardly drove it. No oil puddle or stain on garage floor.
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