If you look around online there seems to be a lot of people saying 2-5 years, including some manufacturers. The last time I spoke with echo they said that there was not a shelf life on their product. I have never seen a two stroke oil with an obvious born on or use by date. It seems to me that lots of dealers buy in bulk as well and may not sell it for many months. If it were truly an item that expired rapidly or to the point that it was of serious concern I figure that the bottles would have more than a batch number; one cannot know how long it was at the dealer and so it is unreasonable to say "two year shelf life" to the consumer if the consumer doesn't know how long it is at the dealer for.
Logically though, if you're buying particularly large containers you probably want to ensure that you shake the remaining quality as some separation of additives over time certainly may occur. So if you're buying like a gallon at a time I'd be sure to shake it thoroughly.
If you want to get to the bottom of it call spectrum specialty oils and ask for Bob. Or call omni specialty packaging. either way.