There's nothing in the article that says they do. They say they get a message from the blood collection agency when they donate and another when their blood is

There's nothing in the article that says they do. They say they get a message from the blood collection agency when they donate and another when their blood is used. I imagine it works pretty much as you suggested below: each bag of blood is identified with a serial number, the collection agency is alerted when that bag is used, this triggers a message from them to the donor. Would you be happy with that?