I knew that at a young age because my grandmother always bought the small box of Nonesuch. I was pretty horrified it had beef suet!Baking mince pies was a holiday tradition in my family. I'm embarrassed to admit it was a LONG time before I realized that the prepared filling we used actually contained beef!!! It always seemed to be nothing more than dried fruit, sugar, and spices.
She would make a pie at Thanksgiving. I kept her last box for years after she died.