I have successfully made apple jelly at Christmas as gifts with juice that I’ve frozen in September. When there’s such bounty from a neighbour’s tree, it’s hard to find the time to do the whole process. So one year, I decided to try processing all those apples just to where the juice had dripped undisturbed for several hours. I’d do a batch in the morning and another at night. It’s amazing how many uses I have found for that wonderful apple juice concentrate!!!
Of course, apples have a lot of pectin. No idea how it would work to make jams and jellies with frozen berries and such. But my freezer book says that “dry-packed” fresh frozen fruit may be used in all recipes much as you would use fresh fruit, adjusting for the amount of sugar used. I think I’d start cooking the fruit before it had completely thawed, because flavour, appearance and texture deteriorate more quickly than with fresh. But that’s just a hunch.