The neighbor list is built using Campus Data Collection. So if this list is incomplete, make sure you have run a recent Data Collection. Additionally, there have been some bugs in earlier versions of Campus Manager. If you're on one of Campus 4.0.12, 5.0.4, or 5.1.1, you might try reinitializing the ANI database, then run a new Data Collection. This can cause missing devices to be found.
The ANI database can be reinitialized with the command: