They probably put them in the post. I only got my letter apologising for losing my details yesterday!
Actually I have a theory that the disks were never lost at all. I suspect the dozy 23 year old didn't actually burn them in the first place. When a fuss was made he just said he had, burned a set and sent them off. I am, of course, totally basing this theory on my 11 years experience of working with young adults who, in my experience, will always lie, even in the face of overwhelming evidence to the contrary, rather than admit to any failing.