Just to clarify, you manually added ONE device to DCR, ran a new Campus Data Collection, and found two new devices on the Topology Map? If so, did Campus Manager Discovery run between the time you added the device to DCR, and the time you checked the map? Discovery will use all devices in DCR as seeds provided none are filtered out. Therefore, it may have located another device, and added it to DCR.

When you delete these devices, Discovery could simply be adding them back. Try disabling Discovery temporarily, then delete the devices and see if they return.