At my LGS they have started used match slips for bigger events such a prereleases. After the event the store has been placing these slips in their scrap paper bin. So they can use the back for notes, life total sheet, etc..
These match slips contain a certain level of information about players, their name and DCI number and signature. I've been thinking about it and there is a possibility this information could be considered sensitive. Thus the store should not reuse these slips there to protect people's information. I've looked through all the rules documents I can find but I can't locate any guidance on this.