.....3 years worth of the various flavoring I prefer but I don't think they will hold up that long
If you mean flavorings for DIY, (not flavors, as in eliquids)...IMO there should be no problem if they're kept away from heat and/or sunlight. I've still got at least 20 or so that I bought Dec. 2015 - Feb. 2016 that are still great. I can't taste nor otherwise sense any difference in them at all as they've aged. They've only been in my flavorings storage cases and/or boxes, in my A/C house...not refrigerated.