Question: If I'm making Homemade Jams/Preserves, how long will they last?

Answer: 
There's also freezer jams, which can easily last a few years in a deep-freeze without losing much quality. They're well sealed, so there's little moisture loss / freezer burn, there's little loss of quality aside from the initial freezing, and you don't have to worry about mold or other organism growing in the freezer.
Home made Jam made with half Fruit and half Sugar will last almost indefinitely... it's additives that spoil food, placed into in a sterile jam jar it could be there many years and still as good as the one eaten in the first week, Ask your granny not a jobsworth! 50/50 nothing else!