According to the vision Rodimus Prime saw, in the past there were eight Constructicons, though in their other appearances they are six. No explanation is given to what happened to the remaining two. See more
[Having entered the Matrix
Where am I? Is this the Matrix?
[a vision of Primon appears before Rodimus
Rodimus Prime, you have embarked on a journey into Cybertron's distant past. Prepare to look into the face of your creator. Eon ago, Cybertron was a factory built by the Quintessons to manufacture robots. There were two product lines: military hardware and consumer goods. These two product lines were the linear ancestors of the Decepticons and the Autobots. In time, the Quintessons endowed ...