Unfortunately, we don't have data on degradation effect of leaving it at 100%. We know it is worse than leaving it at 50% but don't know how much worse. So the advice of others is good - only charge to 100% when you need a full charge and don't let it sit at 100%. We just don't know how much it matters.
Also unfortunately, we don't know how many different battery chemistries there are/were. Did they change sometime in 2013? Or in mid 2014? Or when? Did they change it again and not tell us? Was there a change in 2012 that no one knew about?
From Nissan's perspective, we don't have any need to know and telling us these details would invite more questions. Heaven forbid that we should be informed consumers and know what we are getting.
But realistically, if they switch from one maker to another on any part in the car, the buyer really has no need to know. They probably change brake pad vendors, bolt vendors, bumper vendors, etc, more often than we would like to know, for quality, cost and delivery reasons. When you buy replacement parts, you might find part numbers with a "-1" or "-2" suffix and are told that they are the same part. Yea, right, then why did the part number change?.
In an EV, the battery is far more fundamental. Changing battery vendor or battery recipe is a big deal to geeks like us but Nissan isn't trying to appeal to geeks. They are trying to appeal to the average car buyer. To the average consumer, it's a car with an engine (electric motor) and a fuel tank (battery), limited range, low maintenance, and a tax rebate.
I think Nissan would sell many more Leafs if they did market to more technology-aware folks. Give lectures at universities to budding engineers about what's inside and how it works. Exploit social media with technical information as well as marketing. Then watch EV sales soar to the huge community of people just coming out of college, many buying their first car or first new car.