I've made various refrigerator fruit jams and marmalades, and recipes always say that they will keep in the fridge for about a week or two. But I've kept some for far longer than that -- several months, possibly up to a year in the case of a shockingly good seville orange marmalade (beginner's luck, have never quite matched that first batch), with no apparent ill effects from eating them. And I've done the same with store-bought jams that contain no preservatives (other than the sugar) -- they generally seem fine for a long time.
So why are the cookbooks so conservative about their estimates about keeping times? I do sterilize the jars and closures pretty carefully, I use a clean spoon every time I dip into the jam, but am I just missing something? Is there any nastiness that wouldn't make itself known (by a bad smell, mold, etc.) in this kind of jam? Have I just been lucky in avoiding some kind of silent killer?? Or are the cookbook authors/publishers just trying to avoid lawsuits?