Snippet about petrol storage and how quick it spoils,

[iaaems]

I have come across vehicles that have been left for long periods. They all started and all ran on the existing fuel in the tank - both gasoline and diesel.
My experience of oil companies spans some twenty years. Their chemists will be highly qualified and speak with authority on their subject.
However they will be talking in a sales environment, encouraging you not to store but to buy as and when you need. They will also be talking about ideal situations as well as worst case scenarios. Ideal as in fuel cap on vehicle/container. Worst case scenario cap left off. Cap left off, air gets to product and deterioration happens rather more quickly than if the cap is left on. Climate will also come into play.
The info given is useful and worthy of study but, in my opinion, is only there as quality guidance as opposed to rigid stats and rules.