This reminds me of a story my mum told me.
My grandmother was friends with a woman called Mary, they were friends for 40+ years and really close. Mary had a few family recipes for the most amazing jams, pickles and chuckneys, apparently they were so lovely people would look forward to birthdays and Christmas just to receive a jar of something as a gift.
Supposedly they family had been well known for them for generations.
My GP particularly loved her strawberry jam, and had asked her friend for the recipe many times over the years but had always been told it was a family secret.
My mum grew up with Mary's DD and they have been friends their whole lives.
When Mary passed away she gave her DD, Sue, her families secret preserve recipes and made her swear never to share them with anyone outside of the family.
My GM was really sad when Mary died. Sue, being the lovely woman that she is, came to my GM and said as she considered her family she wanted to share the 'secret family recipes' with her.
It turned out for several generations the family had been buying jams, pickles and chuckneys emptying the jars into a pan, adding a few spices and a bit of sugar bringing it to the boil and then putting it into new jars with their own labels.
My mum and Sue are still friends and still joke about Mary's preserves.
Because of this whenever anyone says that it is a family secret recipe I always assume that it is shop bought and passed off as homemade.