As far as I know, 2 stroke oil does not have an appreciable shelf life. I have some large quantities of Amsoil-racing synthetic that is now over 10 years old as well as some standard 2-stroke oils in the 16 oz bottles that were purchased at about the same time, and both look, smell, and burn just the same as they did the day I bought them… not exactly a scientific analysis I know, but the proof seems to be in the performance.
Pre-mix with synthetic get’s burned up and not stored due to possible deterioration of some rubber components exposed to the fuel, that I have seen damaged, although I have only noted swelled and soft rubber components on the cheaper equipment like snow-blowers, chain saws, weed whackers and the like. If it is pre-mix with standard oil, I try to leave only about a half tank of fuel over the winter, and then top it off, and agitate with fresh pre-mix in the spring, although this is probably just paranoia on my part.
To “winterize” we generally “fog” the insides of the cylinders with 2-stroke oil. The only purpose here is to prevent corrosion or rust from forming on the cylinder walls during storage. With the snowmachines, I generally forgo this, and simply fire them up every month or so during the summer but that is not always possible with an outboard given the necessity for water lubricating the water pump.
Sorry, but I don’t know enough about outboards to say about transportation position and water entrapment….