When you notice that an item is missing (having looked for it more than once, checking the shelf around its supposed location carefully just in case it’s been misfiled), go ahead and mark that puppy as missing! Please, though, leave an x-note in the item record so that we know when it was marked missing, who marked it missing, and any other relevant information that you think should be added. For example: “Marked missing by HS on 5/8/11. Have checked shelf 3 times.” If we don’t have an x-note like this, it’s difficult for us to determine when something was first discovered to be missing; dates like “last checkin” and “last updated” can be misleading.
If you have any questions, please ask!