User blog comment:Master Sima Yi/Assassinews 08-02-'13 — Next game will be all new, plus DLC promotional material/@comment-77.45.54.119-20130214113918/@comment-1153722-20130214142003

You seem to forget that we don't know under what circumstances these memories are available. If there would be any canon explanation for it, then it would be altered memories, like how Daniel's memories were altered during his youth during Vidic's experiments.

Also the fact that this DLC will run parallel to the original story and completely contradicts the original events should make it very clear that this DLC is an alternate reality, not part of the main canon.