Sandbender, I'm really curious...how the hang does the jam reduce in volume if it's sealed in the jar ?
I always make too much (average is over 60 jars a year, seven or eight varieties; it's not unknown for me to make over 100 jars a year; not quite up to BR's numbers, but still a fair amount to share around

) and there's always some old jars stashed in the pantry. There's gooseberry there that's six years old; I opened a jar of it a fortnight ago and it was perfect

but it hadn't shrunk any, iimmc. The wax seal, the cellophane outer seal and the lid on top were all as neat and tidy as the day I made the jam.
So far this year I've made lemon jelly, rhubarb and ginger jam, rhubarb and strawberry jam, raspberry jam and jelly, blackcurrant jam and jelly, and I'm eyeing up brambles and rowans and apples, and maybe another batch of something or other with the rhubarb which has put on another flush of stems in this beautiful weather. There'll be local plums and damsons later on next month too
I also make syrups from raspberries, wild strawberries, elderflowers, blackcurrants and brambles, and I boil down the fruit juices to make apple and pear spreads.
Occasionally, if the local supermarkets have a sell off of the little crates of apricots or peaches, I'll make apricot jam too; I'm fond of that

but they don't grow here.
Cherries I love fresh, or glacé, but I'm not fond of them cooked except in a Madeira cake

I'm playing around with the idea of making some in alcohol though to use in mignardises and chocolates.
Couple of oatcakes, a scrape of jam and a wee thin sliver of rich cheddar ....food of the Gods.
cheers,
Toddy