If you wanted 100% lie-flat then book a JFK-LAX-SEA (or SFO). It's not like you were kicked off the flight and offered a JFK-CVG-SLC-SEA routing all in Y in the middle seat. The flight is advertised for Lie Flat but that isn't what happened. There is really no way to tell. Since this isn't a D1 flight you are just outta luck. Next time remeber that not all things are gaurenteed.