When granny made jelly, she never used water bath canner or sure jell. Just the juice and sugar cooked till it was the right stage on the spoon.
She put the jelly in the hot sterile jars. Then topped it with melted paraffin. Put a sterile lid on it, and as it cooled the a vacuum seal was made.
She gave me a case of jelly from the last batch she ever made. I only opened 1 jar per year at Christmas. The last jar-12 years later was perfectly good.
I remember (as a kid) paraffin wax on top of some jelly in jars! My aunt used to do that - probably learned it from my granny, but I don’t know for sure.