I don't know if this is germane to 2-stroke oil, but the company that services the air compressors at my job recently changed suppliers on the oil they supply/use. After a year or two in storage one of the additives can begin to precipitate out and you MAY lose functionality of that particular additive.
In the case of the air compressor oil, it was an anti-foaming compound, but what if it was the Calcium or Zinc anti-scuff compounds in the 2-stoke oil? A few users running the ragged edge would experience failures that fresh oil would protect against and the oil supplier would be liable.
Chances are that most of us could use that Mobil oil for another 20 years and never experience difficulties, but Mobil marketed that oil to a wide range of users, some of which place some pretty hard demands on their motors. I don't have any around right now, so I'm safe: makes it easy for me, LOL!