I have some Montblanc Midnight Blue ink that I bought 4 and a half years ago. I actually know that because I remembered getting it on Amazon and just looked up the order. I've never taken to it that much, because I was expecting more of a blue black, and when this dries, it just looks black, so there's plenty of it left. But I was thinking of giving it another shot the next time I fill a pen. I just noticed, though, that there is a paper tag on the bottom of the bottle which says September 2017. Is that a "best by" date? I've never run into this on an ink before, generally assuming that it's good until it evaporates or develops mold. But is Montblanc suggesting that you ought to use it before it's too old? It's not that I'm really worried about it having gone bad somehow. Just curious about the logic of putting that date on there.