To quote O'Brien "I hate temporal mechanics"
"Regeneration" is one of those things that creates a paradox that cannot really be untangled. The real question is, were the attacks along the Neutral Zone a random scout and recon mission by the Collective, or was it a result of the signal sent by the drones in "Regeneration"?
In my novelization of "The Best of Both Worlds" it's the latter.
If the second is true, then it was the Borg themselves who understood the complexities of the timeline (which the Queen and Seven of Nine both imply) and, realizing their second attack upon Earth was going to fail, "reset" the timeline into a loop by launching the sphere and giving them endless opportunities to successfully assmilate Earth. The Borg do not seem to regard a temporal directive. Being able to open temporal vortexes gives them a million changes to take the Alpha Quadrant.
Actually, I figure that the message (and the reason for the Borg going back in time in FC) was more about sending the Borg of the past information about the future.