Nobel and the other guard troops were not present at the time of Cold's death and Frieza's first death. As such he was unaware that the Dragon Team even existed, only being aware that Frieza and Cold had been killed upon invading Earth, after having the planet scouted and discovering the "strongest man" Mr. Satan he and the other guard troops chose not to invade until he was dead, as they knew they could not deal with the one who defeated Frieza.
After Mr. Satan's death, the guard troops finally ordered the invasion of Earth in Age 820, leading to a full planet-wide conflict and many deaths, and finally culminating in a battle between the aged Z Fighters and the Frieza Force, Nobel survived the conflict and continued to act as a commander for the Frieza Force remnants years later.
Bomb King Nobel faced the Time Patrollers in Age 1000 and was defeated.
As a member of Frieza's guard troops, Nobel should be powerful enough to defeat the entire Ginyu Force by himself, and hold his own against Frieza's basic level of power in his final form. In Age 820, the guard troops noted that they would be no match for someone who could defeat Frieza.