The airflow through the drives will tend to suck dirt in to them. These correspond to the 8 possible SCSI ID's on each SCSI card. I have found that the only secure method of changing CD's is to completely down the server, exit to DOS, switch out CD's and then cold-boot. CD's usually come with strange volume labels that are hard to remember. In addition, CD's that are part of a subscription series will have different volume labels every month.
Users get tired of tracking all the changed volume names.
This will allow fixed volume labels that don't change. This takes into account all idiosyncrasies of the driver stack, and forces a rebuild of the index and rename of the volumes on boot. This also allows the least amount of editing of the autoexec.ncf when CD's are changed. Allow the server to boot and make sure that all CD drives have CD's in them. Then load the statements by hand, while observing the console and CD's drive lights.