Dates are really only a general guideline when it comes to eliquids and flavorings. I've had some go bad long before they should have, and others last much longer than the expected lifetime. Part of it depends on the chemicals in it and part of it depends on how it's stored. If it still smells right and looks good, then it should be fine. From my experience, the most likely thing to happen is for the flavor to lose some of its flavor notes and become weak or dull.