I think there's some controversity regarding the continuity between the (inofficial) first contact between humans and the Borg in ENT ("Regeneration") and in TNG ("Q Who"). It's been a while since I watched the ENT Borg episode and the TNG Borg episodes, but if I remember correctly, "Regeneration" ended with the Enterprise crew discovering that the Borg they defeat send information about humanity to the collective. It's stated that this information will reach them probably in the 24th century and might lead to an invasion. So, this is actually what we see then in TNG. In the 24th century, the Borg know about humanity and invade them. So you could think that this ENT episode was intended not to break the continuity set up already in TNG. However, if I remember it right, it was presented in TNG as if the Borg took note of humanity because of the encounter with the Enterprise in "Q Who", not because of the information they received from those Borg from the 22nd century in "Regeneration". Since both events are presented in ST shows and are thus canon, what do you think made the Borg discover humanity? Both version actually seem to contradict each other, either they took note of humanity because of the encounter with Archer's Enterprise or Picard's. Or could it be that both events (the Borg encountering Picard's Enterprise and receiving the information from the 22nd century Borg) took place at more or less the same time so both played a role?