Pseudocanon

Transformers fiction has an unusual but fairly cut-and-dried policy on what is canon: anything depicted by official fiction/sourcebooks is canon (for some continuity at least). However, there is a large amount of additional information about the various Transformers universes that does not come from officially-endorsed products. Background gleaned from creator interviews, early drafts of stories, forum posts, and the like all falls into the realm of pseudocanon.

Pseudocanon usually fits in well with the actual canon (at least until a later writer invalidates it), as it is the writers' idea of "what is really going on" as they craft their stories. However, because it is not established in any official fiction, it can't be taken as a given or definitely "true". Fans are free to incorporate pseudocanon, or not, into their personal canons as they see fit. Knowledge of relevant pseudocanon may enhance one's enjoyment of a story, but can't be used to "prove" a point about that story because the pseudocanon itself is not in the story.

As an example, at the end of Beast Wars, the Maximals depart from Earth, without ever being shown replacing the spark of the original Megatron. Although it could be presumed that they had done so, it was not established as true. The show's writers stated that yes, the Maximals had indeed replaced the spark, and that the scene had even been animated before it was cut for time. They even provided a clip of the scene to Ben Yee who posted it on his site. Despite all of this, the return of Megatron's spark is not canonically established. It is clearly the writers' intent for the spark to have been replaced, and again, it is logical to presume that this would have happened off-camera, but because no canon source -- that is, no official and finished fiction -- establishes it, it technically remains "not necessarily true".