No multistatics detected the B-2 and engaged it.

Sure,no multistatics detected B-2,f117 or any other NATO aircraft,because
Serbians had no multistatics.
Even though this fact was well known by everbody,hitting two f117s by SAMs
created a multistatic scare in Washington and led to shutdown of serbian power
system.
(At that time US multistatic system,or the first version of it,was already a
couple of years old,so they were aware of the capabilities of US system)