On two separate projects in two separate companies I have become aware of an issue where AD information from a long time ago, seems to revert back into AD. In case A, a DC had been removed several months prior, and then Bam! it looked like there references in AD to the "flying dutchman" AD server. In case b, the event seems to revolve around a switch reboot. In this case AD information from YEARS ago returned (We think the information coincides to the point when the systems were imaged and first brought into the domain (like 6 years ago)) I did note that one of the DC was not responding to dns queries via nslookup, and workstations on a specific subnet seemed to revert from DHCP subnet IP to a 169 address. Immediately after the event rebooting the workstations still left the system with the 169 addresses. The switches involved are Cisco switches and the subnet has an IP helper for the interface.
I don't have specifics on what happened, I am just trying to understand what causes an event like this.