Question for old time residents?

We need some help trying to find out if someone in 1998 made a master list of all our documents. As you can see in this image there is a four digit number and a July 28 date. We have seen this on most of the documents we have scanned in. Do any of the SP old time residents have any idea what this is?

As some of you may be aware with the help from Doug and Vickie Iverson we are converting our SP paper records into a digital format. We have so far digitized a few thousand pages with much more to complete. It would be great if someone has this master list so we can use this as a way of tracking our old paper copies to our new digitized copies.