The only thing standing between you and mould or worse with unsealed, sterilized jars is the fact that it contains a high volume of sugar. Honey, sugar and highly acidic vegetables like tomatoes or other vegetables canned with vinegar (pickles come to mind) still require the water bath I described, and still needs the jars sterilized before filling.as others have described.
At the least,syrenesis will occur... and you'll have a jar of semiliquid floating on top of really messy stuff.
I wonder why even the highly controlled commercial jellies, preserves and jams have "use by dates"?
Additionally, without being vacuum sealed the dissolved sugar can, at some point, re-crystalize just like honey, when left exposed. I imagine a cling wrap or the "oil cloth" will work to a degree, but it's a small investment to find the correct lids. The reason why old lids can't be reused is because they are originally built with a raised center that depresses when the jars cool causing it to "ping" with it's response to the vacuum underneath...
This might shed light for you:
http://www.canning-fo...cipes.com/canning.htm
I'm just saying...