Another reason to only buy EVOO with a harvest date on the label, is because there will be differences from year to year (just like with wine) that reflects the season. For example, a dry year will produce a much stronger olive oil. So there is nothing wrong with purchasing last seasons olive oil (in some years it may be better than the current years oil) but I would stop short of purchasing anything that is older than that, especially if it is packaged in glass bottle (see below).
So when buying your Olive Oil, make sure you look for two things. A harvest date and the Australian Extra Virgin Certified Logo.
Please note: EVOO in a glass bottle will lose its extra virgin qualities much earlier especially if this glass bottle has been opened or not stored in a dark and cool pantry. Our EVOO will easily last 2 years because it is kept in a triple layered membrane that keeps out all light and air even after you start using it.