To be fair, if the jams are canned it’s important to make sure you have the right amount of sugar and acid to make it safely shelf stable. I make jams every summer to give to family and friends and I still follow the recipes in the box of Pomona’s pectin. The thing I’ve been perfecting over the years is finding the best fruit at the farmer’s market and then processing it (peeling/blending/cooking) it in a way that yields a pleasing jam.