That would make sense, and show further why the engine was labledd "Series 80" when it really was not.
Marketing did not want to go into the 80's with an engine named for the 70's, while the design team was not about to chuck out a new design of engine to fill a gap of about 6 months before the launch of the actual S80 units.
Hey, we still have some old mowers, new stickers anyone?