In Dragon Ball Z, when Goku was fighting Kid Buu, there were many enemies watching him from Hell.
From DBZ Wikia article on Hell:
In the Kid Buu Saga, during the fight with Kid Buu, the ogres are seen watching the fight alongside Cell, Frieza, King Cold, Recoome, Burter, Jeice, Guldo, Dr. Gero, Appule, and Babidi.
However, when Frieza was revived, he didn't know about the fight with Majin Buu.
Is there any reason as to why this is so?