An issue list is a special type of SharePoint list. Each time an issue is update, a historical list item is added to the list. The actual ID of the current issue item therefore never changes. The current item is flagged by an “IsCurrent” boolean field (read only via the SharePoint object model).
I initially thought that historical entries would be related via a guid based linked list; however this is not the case. When an issue is created, the issue is given 2 guids – one is the standard listitem “GUID” identifier (possessed by all list items in SharePoint) and the other “Related ID” is used to link related records. The related id stays constant over both the current and historical entry for an issue. The sequence of historical items is simply maintained by the time created or sequence within ids (I’m not sure which, and I guess its not important).
A basic example of how to add / update an issue using the SharePoint object model is available at http://net.bloggix.com/PermaLink,guid,aa4c6b98-2039-432b-af80-b8baf901fdf2.aspx