Spoiler So, when FOC Optimus knocks the Dark Spark into space, it crosses universes, but it's still bound by time, so it exists for eons in the movie-verse, legends are heard of it, it eventually comes to Earth. When Optimus faces Lockdown at the end of the game, he knocks it into the time bridge, which sends it back in time, where it eventually then crosses into a third universe, the G1 universe. My theory! Although for it to work that way, all the universes must have their events aligned a bit.