I suppose, technically speaking, it's possible to have the 2552-era plot of ILB as canon without including 2004, but ultimately the successful ending of the Covenant 'spy' ai and resolution of the conflicts within Melissa's construct itself, were due to the efforts of those she interacted with during her slipspace-caused dual existence in 2004; additionally, it was due to the 'one hand not knowing what the other was doing' that provided covert surveillance of the individuals related to Melissa in 2552, and discover key pieces of information that led to the successful reactivation of the artifact and end of the Flea. Her dual existence due to the Forerunner artifact is sort of key to the plot conflict resolution... and time/relativity effects of slipspace were technically already canon.

I always understood the Forerunner artifact as having an unexpected space/time effect, dramatically enhanced when activated within slipspace. That point alone opens a can of worms for potential plots and stories :)