sixdogs, This is your thread so you cannot be accused of taking it off topic.
There are enormous differences between cultivars of olives. They are called cultivars and not "varieties". A variety is a naturally occurring variant of a species. A cultivar refers to a cultivated plant that has been specifically chosen for one or more characteristics that are always retained by the offspring of the cultivar. I have a small amount of information on an early blog (25 Nov 2011 titled A glossary followed by a blog on olives) but the easy way is to liken olives to wine grapes. If you are a wine drinker, then you will be aware that there is a huge range of different types, red, white, sweet, dry and every variation in between, and that different grapes make different wines. Similarly different olives make different oils.
Time of harvest makes a big difference too. It varies between countries (northern hemisphere) from late October, right through to the end of winter and even spring in places like Liguria in Italy that is close to the French border and not too far away from Nice, where they leave the same cultivar on the trees until then too. In France it is known as Calletier (not certain I have the spelling right) and other names in Italy. It is the olive found in Niçoise salad (ie Nice salad - pronounced niece not nice). Tuscany in southern Italy picks its olives much earlier and so produces a much different oil. It is the same all around the world where olives are grown, early or late harvest according to tradition. Olives ripen before they change colour - they alll begin green. Some never change from green, but that is not common, others turn red or purple, or mottled and others become completely black.
You should be aware that according to some tests done by UC Davis, 2011 or 2012, more than half the extra vrigin olive oils of well over a hundred tested were not what they claimed to be. Olive oil appears to have been open to adulteration forever. I remember reading at one time that Italy exported more oil than it produced. Portugal imports a lot. As a consumer, I am sure it is not that important to you if a slightly higher acid oil has been added (similar to blending wines or whiskies) if the end result tastes pleasant to you as an individual and you are happy with the price you paid for it. On the other hand if you are paying the sort of outrageous prices I see on the Internet, tens of dollars and even more than $300 a bottle, then you should be getting what it says on the label. Quite frankly, I am certain that no oil is worth these prices. Like most people in Portugal we hand pick, the olives are milled and pressed in a local mill, and I like the result. I do not yet have enough production from the young trees to market my own oil direct, so I am reluctant to put a price on what I think it is worth, but I know it is not hundreds of dollars a bottle.