From the Lookup (Subs) screen you can select any subscription and click the 'Issues served' button to see a list of all of the issues that were served to that subscription.
The list is arranged as a series of blocks of issues, each with a starting and ending issue number. Each block represents a contiguous set of issues that were served with the same number of copies per issue and the same service code. If the service code of the subscription changes (perhaps because the subscriber switched from edition to another) then a new block of issues is started. For audited publications a new block is also created whenever the classification or request type changes.
On some blocks of issues served you may also see a 'D' in the 'Drop' column. This is used by the audit system to signal that one person was substituted for another on the subscription and that both a removal and an addition to the circulation list should be reported.
If there are any gaps in service you will also see the reasons such as "Expire (paid)" or "Cancel" listed for the gaps. Please note that you will see reasons listed only where there is a gap in service. This means that the last block in the list will never have a reason listed because the subscription might get renewed, resulting in no gap in service.